diff --git a/.claude/settings.local.json b/.claude/settings.local.json
index 29dfeac..9d47561 100644
--- a/.claude/settings.local.json
+++ b/.claude/settings.local.json
@@ -12,7 +12,29 @@
       "Bash(kill 128755)",
       "Bash(echo \"exit=$?\")",
       "Bash(npm view *)",
-      "Bash(echo \"--- exit $? ---\")"
+      "Bash(echo \"--- exit $? ---\")",
+      "Bash(rm -rf /tmp/nas-test)",
+      "Bash(mkdir -p \"/tmp/nas-test/AAA = ACTIVE/Test Biz GmbH/docs/subdir\")",
+      "Bash(mkdir -p \"/tmp/nas-test/AAA = ACTIVE/Test Biz GmbH/.git\")",
+      "Bash(ln -s /etc/passwd \"/tmp/nas-test/AAA = ACTIVE/Test Biz GmbH/escape.pdf\")",
+      "Bash(mkdir -p \"/tmp/nas-test/AAA = SOLD\" \"/tmp/nas-test/AAA = INACTIVE\")",
+      "Bash(break)",
+      "Bash(node -pe 'JSON.parse\\(require\\(\"fs\"\\).readFileSync\\(0\\)\\).[0].id')",
+      "Bash(curl -s localhost:8090/api/staff)",
+      "Bash(pkill -f 'tsx.*server')",
+      "Bash(curl -s -m 2 -o /dev/null -w '%{http_code}\\\\n' localhost:8090/api/health)",
+      "Bash(/tmp/claude-1000/-home-aknuth-git-bizmatch-app/4b67ffa5-f538-477a-ae54-6d68ec7ee19c/scratchpad/run-server.sh *)",
+      "Bash(docker run *)",
+      "Skill(claude-in-chrome)",
+      "Bash(/tmp/claude-1000/-home-aknuth-git-bizmatch-app/4b67ffa5-f538-477a-ae54-6d68ec7ee19c/scratchpad/run-vite.sh *)",
+      "Bash(curl -s -m 2 localhost:8090/api/health)",
+      "Bash(ps -eo pid,etime,cmd)",
+      "Bash(curl -s localhost:8090/viewer/pdf_viewer.js)",
+      "Bash(echo \"QC occurrences served: $?\")",
+      "Bash(kill 29669 29703 29714)",
+      "Bash(curl -s -m 2 -o /dev/null -w 'server: %{http_code}\\\\n' localhost:8090/api/health)",
+      "Bash(git check-ignore *)",
+      "Bash(git add *)"
     ]
   }
 }
diff --git a/.dockerignore b/.dockerignore
index af59045..3fd0c84 100644
--- a/.dockerignore
+++ b/.dockerignore
@@ -4,3 +4,4 @@ web/node_modules
 web/dist
 .env
 .git
+web/public/pdfjs
diff --git a/.gitignore b/.gitignore
index 2068d28..dc73701 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@ dist/
 web/node_modules/
 web/dist/
 .env
+web/public/pdfjs/
diff --git a/README.md b/README.md
index 6deda93..640ddb4 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,8 @@
 
 Module 1: foundation (Docker Compose, PostgreSQL, schema, migrations, login).
 Module 2: business scan (NAS -> DB) and the first UI.
+Module 3: recursive file listing, PDF streaming from the NAS and the ported
+pdf.js viewer.
 
 The UI and all domain constants are English.
 
@@ -83,7 +85,7 @@ directory aborts the scan with an error naming the path.
 3. Copy the project folder to the AI machine, run `docker compose up -d --build`
 4. Restore the dump: `docker compose exec -T db psql -U bizmatch bizmatch < backup.sql`
 
-## API (as of module 2)
+## API (as of module 3)
 
 | Method | Path                        | Purpose                                          | Session |
 | ------ | --------------------------- | ------------------------------------------------ | ------- |
@@ -96,22 +98,74 @@ directory aborts the scan with an error naming the path.
 | POST   | /api/businesses/scan        | scan the NAS → `{scanned, inserted, updated, missing}` | yes |
 | GET    | /api/businesses             | list `?status=&search=` + counts per status      | yes     |
 | GET    | /api/businesses/:id         | single business incl. `nas_path`                 | yes     |
-| GET    | /api/businesses/:id/files   | live directory listing (PDFs first)              | yes     |
+| GET    | /api/businesses/:id/files   | recursive listing, max depth 3 (PDFs first)      | yes     |
+| GET    | /api/businesses/:id/file    | stream one file, `?path=<relative>`              | yes     |
 
 Everything except health, staff (GET+POST) and login requires the session
 cookie; without it the API answers `401`.
 
+### File listing and streaming
+
+`/files` walks the business directory recursively (max depth 3), skipping
+dotfiles, dot-directories and symlinks, and returns
+`{ path, size, mtime }` with `path` relative to the business directory and
+always posix-separated. PDFs come first, then everything else, each group
+alphabetical.
+
+`/file?path=…` streams one of those files straight from disk
+(`createReadStream`, never buffered):
+
+* the path is resolved against `nas_path` and then `realpath`-validated to be
+  inside `realpath(business dir)`. Absolute paths, `..`, leading dots, empty
+  paths and symlinks pointing out of the tree get `400`; a missing file `404`.
+* single-range HTTP `Range` requests answer `206` with `Content-Range`,
+  unsatisfiable ones `416`.
+* `ETag` is derived from mtime + size, `If-None-Match` answers `304`.
+* `.pdf` is served as `application/pdf` (inline), anything else as
+  `application/octet-stream` with `Content-Disposition: attachment`.
+
 ## Frontend
 
 `web/` is a Vite + React + TypeScript app with Tailwind v4 (no router, no state
 library). Views: login ("Who is working?"), business list (tabs with counts,
-search, "Scan NAS now") and business detail (status badge, live file list).
+search, "Scan NAS now") and business detail — a master-detail split filling the
+viewport: file table left, PDF viewer right.
 
 In dev, Vite proxies `/api` to `http://localhost:8090`. In production the
 Fastify app serves `web/dist` via `@fastify/static` with an SPA fallback to
 `index.html` for all non-`/api` routes; the Dockerfile builds the frontend in
 its own stage and copies `web/dist` into the runtime image.
 
+### PDF viewer
+
+The viewer is the proven one from the phase-1 Deno desktop app (see
+`viewer-phase1/`), ported nearly byte-identical. It lives in
+`web/public/viewer/` as plain, unbundled ES modules — Vite serves `public/`
+as-is, so the same files work in dev and prod. The React app embeds it in an
+`<iframe>`:
+
+```
+/viewer/index.html?file=<urlencoded /api/businesses/:id/file?path=...>
+```
+
+The page refuses any `file` value that is not a root-relative `/api/` path, and
+the iframe is same-origin, so the normal session cookie authenticates it.
+
+`web/public/pdfjs/` holds the pdf.js runtime, copied out of
+`node_modules/pdfjs-dist` (pinned to exactly 6.1.200) by
+`web/scripts/copy-pdfjs.mjs`, which runs on `predev` and `prebuild` — also
+inside the Docker web stage. The directory is generated and git-ignored:
+
+```
+web/public/pdfjs/legacy/         pdf.min.mjs + pdf.worker.min.mjs
+web/public/pdfjs/wasm/           CCITT-G4/JBIG2, JPEG2000 and ICC decoders
+web/public/pdfjs/standard_fonts/ standardFontDataUrl
+web/public/pdfjs/iccs/           iccUrl
+```
+
+The `wasm/` directory is what makes scanned B/W pages render at all; without it
+pdf.js fails the decoders silently and shows blank white canvases.
+
 ## Structure
 
 ```
@@ -120,10 +174,14 @@ src/
   config.ts           env configuration
   db.ts               pg pool + query helpers
   migrate.ts          migration runner (transactional, advisory lock)
-  business-scan.ts    NAS scan + directory listing
-  server.ts           Fastify app (health, staff, login, businesses, static)
+  business-scan.ts    NAS scan, recursive listing, safe file path resolution
+  server.ts           Fastify app (health, staff, login, businesses, file, static)
 web/
+  scripts/copy-pdfjs.mjs  pdfjs-dist -> public/pdfjs/ (predev + prebuild)
+  public/viewer/      standalone, unbundled pdf.js viewer page
+  public/pdfjs/       generated, git-ignored pdf.js runtime
   src/api.ts          typed API client
   src/App.tsx         session gate + view switch
   src/views/          Login, Businesses, BusinessDetail
+viewer-phase1/        reference copy of the phase-1 desktop viewer
 ```
diff --git a/src/business-scan.ts b/src/business-scan.ts
index e2031c1..3521e82 100644
--- a/src/business-scan.ts
+++ b/src/business-scan.ts
@@ -1,4 +1,4 @@
-import { readdir, stat } from 'node:fs/promises';
+import { readdir, realpath, stat } from 'node:fs/promises';
 import path from 'node:path';
 import { config } from './config.js';
 import { query } from './db.js';
@@ -103,23 +103,101 @@ export async function scanBusinesses(
 }
 
 export interface BusinessFile {
-  name: string;
+  /** Relative to the business directory, always with posix separators. */
+  path: string;
   size: number;
   mtime: string;
 }
 
-/** Live, non-recursive listing of a business directory: PDFs first, then the rest, alphabetical. */
-export async function listBusinessFiles(nasPath: string): Promise<BusinessFile[]> {
-  const entries = await readdir(nasPath, { withFileTypes: true });
-  const files: BusinessFile[] = [];
+/** How deep below the business directory the listing descends. */
+const MAX_DEPTH = 3;
+
+async function walk(root: string, relative: string, depth: number, out: BusinessFile[]) {
+  const entries = await readdir(path.join(root, relative), { withFileTypes: true });
   for (const entry of entries) {
-    if (!entry.isFile()) continue;
-    const info = await stat(path.join(nasPath, entry.name));
-    files.push({ name: entry.name, size: info.size, mtime: info.mtime.toISOString() });
+    if (entry.name.startsWith('.')) continue; // dotfiles and dot-directories
+    const rel = relative ? `${relative}/${entry.name}` : entry.name;
+    if (entry.isDirectory()) {
+      if (depth < MAX_DEPTH) await walk(root, rel, depth + 1, out);
+      continue;
+    }
+    if (!entry.isFile()) continue; // symlinks, sockets, ... are not listed
+    const info = await stat(path.join(root, rel));
+    out.push({ path: rel, size: info.size, mtime: info.mtime.toISOString() });
   }
-  const isPdf = (name: string) => name.toLowerCase().endsWith('.pdf');
+}
+
+/**
+ * Live, recursive listing of a business directory (max depth 3): PDFs first,
+ * then the rest, each group alphabetical by relative path.
+ */
+export async function listBusinessFiles(nasPath: string): Promise<BusinessFile[]> {
+  const files: BusinessFile[] = [];
+  await walk(nasPath, '', 1, files);
+  const isPdf = (p: string) => p.toLowerCase().endsWith('.pdf');
   return files.sort((a, b) => {
-    if (isPdf(a.name) !== isPdf(b.name)) return isPdf(a.name) ? -1 : 1;
-    return a.name.localeCompare(b.name);
+    if (isPdf(a.path) !== isPdf(b.path)) return isPdf(a.path) ? -1 : 1;
+    return a.path.localeCompare(b.path);
   });
 }
+
+/** Thrown by resolveBusinessFile; `status` is the HTTP status the route should answer with. */
+export class BusinessFileError extends Error {
+  constructor(readonly status: 400 | 404, message: string) {
+    super(message);
+  }
+}
+
+export interface ResolvedFile {
+  /** Absolute, symlink-resolved path — safe to open. */
+  absPath: string;
+  size: number;
+  mtimeMs: number;
+}
+
+/**
+ * Turns a client-supplied relative path into an absolute path inside the business
+ * directory. Rejects empty/absolute paths and "..", then realpath-validates that
+ * the result really is below realpath(business directory), which also catches
+ * symlinks pointing out of the NAS tree.
+ */
+export async function resolveBusinessFile(
+  nasPath: string,
+  relPath: unknown,
+): Promise<ResolvedFile> {
+  if (typeof relPath !== 'string' || relPath === '') {
+    throw new BusinessFileError(400, 'path is missing');
+  }
+  if (relPath.includes('\0')) throw new BusinessFileError(400, 'invalid path');
+  if (relPath.startsWith('/') || relPath.startsWith('\\') || /^[a-zA-Z]:/.test(relPath)) {
+    throw new BusinessFileError(400, 'absolute paths are not allowed');
+  }
+  // Both separators, so a "..\\.." variant cannot slip past on any platform.
+  // Rejecting every leading dot covers "." and ".." and keeps the endpoint in
+  // sync with listBusinessFiles(), which skips dotfiles and dot-directories.
+  const segments = relPath.split(/[/\\]/);
+  if (segments.some((s) => s === '' || s.startsWith('.'))) {
+    throw new BusinessFileError(400, 'invalid path segment');
+  }
+
+  let base: string;
+  try {
+    base = await realpath(nasPath);
+  } catch {
+    throw new BusinessFileError(404, 'business directory not found');
+  }
+
+  let absPath: string;
+  try {
+    absPath = await realpath(path.join(base, ...segments));
+  } catch {
+    throw new BusinessFileError(404, 'file not found');
+  }
+  if (absPath !== base && !absPath.startsWith(base + path.sep)) {
+    throw new BusinessFileError(400, 'path escapes the business directory');
+  }
+
+  const info = await stat(absPath);
+  if (!info.isFile()) throw new BusinessFileError(404, 'file not found');
+  return { absPath, size: info.size, mtimeMs: Math.floor(info.mtimeMs) };
+}
diff --git a/src/server.ts b/src/server.ts
index 4f29521..c06f6a8 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -1,4 +1,4 @@
-import { existsSync } from 'node:fs';
+import { createReadStream, existsSync } from 'node:fs';
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
 import Fastify from 'fastify';
@@ -7,7 +7,12 @@ import fastifyStatic from '@fastify/static';
 import { config } from './config.js';
 import { pool, query, queryOne } from './db.js';
 import { runMigrations } from './migrate.js';
-import { listBusinessFiles, scanBusinesses } from './business-scan.js';
+import {
+  BusinessFileError,
+  listBusinessFiles,
+  resolveBusinessFile,
+  scanBusinesses,
+} from './business-scan.js';
 
 interface Staff {
   id: string;
@@ -169,6 +174,83 @@ app.get<{ Params: { id: string } }>('/api/businesses/:id/files', async (req, rep
   }
 });
 
+/** Parses a single-range `Range` header. null = ignore, 'invalid' = 416. */
+function parseRange(
+  header: string | undefined,
+  size: number,
+): { start: number; end: number } | null | 'invalid' {
+  if (!header) return null;
+  const match = /^bytes=(\d*)-(\d*)$/.exec(header.trim());
+  if (!match) return null; // multi-range or garbage: answer with the full body
+  const [, rawStart, rawEnd] = match;
+  if (rawStart === '' && rawEnd === '') return 'invalid';
+
+  let start: number;
+  let end: number;
+  if (rawStart === '') {
+    // suffix range: the last N bytes
+    const suffix = Number(rawEnd);
+    if (suffix === 0) return 'invalid';
+    start = Math.max(0, size - suffix);
+    end = size - 1;
+  } else {
+    start = Number(rawStart);
+    end = rawEnd === '' ? size - 1 : Math.min(Number(rawEnd), size - 1);
+  }
+  if (start > end || start >= size) return 'invalid';
+  return { start, end };
+}
+
+app.get<{ Params: { id: string }; Querystring: { path?: string } }>(
+  '/api/businesses/:id/file',
+  async (req, reply) => {
+    const row = await queryOne<Business>('SELECT * FROM business WHERE id = $1', [req.params.id]);
+    if (!row) return reply.code(404).send({ error: 'business not found' });
+
+    let file;
+    try {
+      file = await resolveBusinessFile(row.nas_path, req.query.path);
+    } catch (err) {
+      if (err instanceof BusinessFileError) {
+        return reply.code(err.status).send({ error: err.message });
+      }
+      throw err;
+    }
+
+    const etag = `"${file.mtimeMs.toString(16)}-${file.size.toString(16)}"`;
+    reply.header('ETag', etag);
+    reply.header('Accept-Ranges', 'bytes');
+    reply.header('Cache-Control', 'private, max-age=0, must-revalidate');
+
+    const ifNoneMatch = req.headers['if-none-match'];
+    if (ifNoneMatch && ifNoneMatch.split(',').some((t) => t.trim().replace(/^W\//, '') === etag)) {
+      return reply.code(304).send();
+    }
+
+    const range = parseRange(req.headers.range, file.size);
+    if (range === 'invalid') {
+      reply.header('Content-Range', `bytes */${file.size}`);
+      return reply.code(416).send({ error: 'range not satisfiable' });
+    }
+
+    const name = (req.query.path ?? '').split('/').pop() ?? 'file';
+    const isPdf = name.toLowerCase().endsWith('.pdf');
+    const filenameStar = `filename*=UTF-8''${encodeURIComponent(name)}`;
+    reply.header('Content-Type', isPdf ? 'application/pdf' : 'application/octet-stream');
+    reply.header('Content-Disposition', `${isPdf ? 'inline' : 'attachment'}; ${filenameStar}`);
+
+    if (range) {
+      reply.code(206);
+      reply.header('Content-Range', `bytes ${range.start}-${range.end}/${file.size}`);
+      reply.header('Content-Length', range.end - range.start + 1);
+      return reply.send(createReadStream(file.absPath, { start: range.start, end: range.end }));
+    }
+
+    reply.header('Content-Length', file.size);
+    return reply.send(createReadStream(file.absPath));
+  },
+);
+
 // --------------------------------------------------------------- Static
 // Serves the built frontend in production; SPA fallback for non-/api routes.
 const WEB_DIST = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..', 'web', 'dist');
diff --git a/web/package.json b/web/package.json
index 3e74c21..48e15bc 100644
--- a/web/package.json
+++ b/web/package.json
@@ -4,7 +4,10 @@
   "private": true,
   "type": "module",
   "scripts": {
+    "copy-pdfjs": "node scripts/copy-pdfjs.mjs",
+    "predev": "npm run copy-pdfjs",
     "dev": "vite",
+    "prebuild": "npm run copy-pdfjs",
     "build": "vite build",
     "preview": "vite preview",
     "typecheck": "tsc --noEmit"
diff --git a/web/public/viewer/index.html b/web/public/viewer/index.html
new file mode 100644
index 0000000..f7d4c8b
--- /dev/null
+++ b/web/public/viewer/index.html
@@ -0,0 +1,24 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width,initial-scale=1">
+    <title>PDF</title>
+    <link rel="stylesheet" href="/viewer/viewer.css">
+    <script type="module">
+    // Vite serves public/ verbatim, so this page is unbundled in dev and prod alike.
+    console.log("[BizMatch] PDF.js frontend build: legacy");
+    import * as pdfjsLib from "/pdfjs/legacy/pdf.min.mjs";
+    pdfjsLib.GlobalWorkerOptions.workerSrc = "/pdfjs/legacy/pdf.worker.min.mjs";
+    globalThis.pdfjsLib = pdfjsLib;
+    </script>
+    <script type="module" src="/viewer/pdf_viewer.js"></script>
+  </head>
+  <body>
+    <section class="viewer">
+      <div id="pdfViewer"></div>
+      <div id="pdfMessage">Select a document</div>
+    </section>
+    <script type="module" src="/viewer/viewer.js"></script>
+  </body>
+</html>
diff --git a/web/public/viewer/pdf_viewer.js b/web/public/viewer/pdf_viewer.js
new file mode 100644
index 0000000..7c95003
--- /dev/null
+++ b/web/public/viewer/pdf_viewer.js
@@ -0,0 +1,385 @@
+// PDF.js viewer using pdfjs-dist 6.1.200 legacy build.
+// Depends on global pdfjsLib (loaded in index.html).
+
+const ZOOM_MIN = 0.25;
+const ZOOM_MAX = 5;
+const ZOOM_STEP = 1.2; // multiplicative
+
+class PdfViewer {
+  constructor(container, options = {}) {
+    this.container = container;
+    this.generation = 0;
+    this.loadingTask = null;
+    this.doc = null;
+    this.numPages = 0;
+    this.renderTasks = new Set();
+    this.lastUrl = null;
+    this.lastSize = null;
+    // multiplier on fit-to-width (1 = fit width); can be seeded from the
+    // previous viewer instance so zoom survives switching documents
+    this.zoom = Math.min(
+      ZOOM_MAX,
+      Math.max(ZOOM_MIN, options.initialZoom ?? 1),
+    );
+    this._lastRenderWidth = 0;
+    this._resizeTimer = null;
+    this._zoomTimer = null;
+    this.resizeObserver = null;
+    this._createDOM();
+    this._updateZoomLabel();
+    this._observeResize();
+  }
+
+  _createDOM() {
+    // The pages container is always visible (never hidden).
+    // Loading and error states are overlays on top.
+    this.container.innerHTML = `
+      <div class="pdf-v-toolbar" hidden>
+        <button class="pdf-v-zoom-out" title="Zoom out (Ctrl+mouse wheel)">\u2212</button>
+        <button class="pdf-v-zoom-label" title="Fit to page width">100%</button>
+        <button class="pdf-v-zoom-in" title="Zoom in (Ctrl+mouse wheel)">+</button>
+      </div>
+      <div class="pdf-v-pages"></div>
+      <div class="pdf-v-overlay pdf-v-loading" hidden>Loading PDF\u2026</div>
+      <div class="pdf-v-overlay pdf-v-error" hidden>
+        <div class="pdf-v-error-msg"></div>
+        <button class="pdf-v-retry">Retry</button>
+      </div>
+    `;
+    this.toolbar = this.container.querySelector(".pdf-v-toolbar");
+    this.zoomLabel = this.container.querySelector(".pdf-v-zoom-label");
+    this.pagesDiv = this.container.querySelector(".pdf-v-pages");
+    this.loadingDiv = this.container.querySelector(".pdf-v-loading");
+    this.errorDiv = this.container.querySelector(".pdf-v-error");
+    this.errorMsg = this.container.querySelector(".pdf-v-error-msg");
+    this.retryBtn = this.container.querySelector(".pdf-v-retry");
+
+    this.retryBtn.addEventListener("click", () => {
+      if (this.lastUrl != null) {
+        this._setState("loading");
+        this._loadInternal(this.lastUrl, this.lastSize);
+      }
+    });
+
+    this.container.querySelector(".pdf-v-zoom-in").addEventListener(
+      "click",
+      () => this.setZoom(this.zoom * ZOOM_STEP),
+    );
+    this.container.querySelector(".pdf-v-zoom-out").addEventListener(
+      "click",
+      () => this.setZoom(this.zoom / ZOOM_STEP),
+    );
+    // Clicking the percentage resets to fit-width.
+    this.zoomLabel.addEventListener("click", () => this.setZoom(1));
+
+    // Ctrl + mouse wheel zoom, like in browsers / PDF readers.
+    this.pagesDiv.addEventListener("wheel", (e) => {
+      if (!e.ctrlKey) return;
+      e.preventDefault();
+      this.setZoom(this.zoom * (e.deltaY < 0 ? 1.1 : 1 / 1.1));
+    }, { passive: false });
+  }
+
+  // ---- Zoom ----
+
+  setZoom(zoom) {
+    const clamped = Math.min(ZOOM_MAX, Math.max(ZOOM_MIN, zoom));
+    if (Math.abs(clamped - this.zoom) < 0.001) return;
+    this.zoom = clamped;
+    this._updateZoomLabel();
+    if (!this.doc) return;
+    // Debounce so repeated +/+/+ or wheel ticks trigger one re-render.
+    clearTimeout(this._zoomTimer);
+    this._zoomTimer = setTimeout(() => this._rerender(), 120);
+  }
+
+  _updateZoomLabel() {
+    this.zoomLabel.textContent = `${Math.round(this.zoom * 100)}%`;
+  }
+
+  // ---- Resize ----
+
+  _observeResize() {
+    if (typeof ResizeObserver === "undefined") return;
+    this.resizeObserver = new ResizeObserver(() => {
+      if (!this.doc) return;
+      const width = this._renderWidth();
+      if (Math.abs(width - this._lastRenderWidth) < 2) return;
+      clearTimeout(this._resizeTimer);
+      this._resizeTimer = setTimeout(() => {
+        console.log(
+          `[BizMatch] PDF viewer resized, re-rendering at ${this._renderWidth()}px`,
+        );
+        this._rerender();
+      }, 150);
+    });
+    this.resizeObserver.observe(this.container);
+  }
+
+  _renderWidth() {
+    return Math.max(Math.round(this._getViewportWidth() * this.zoom), 100);
+  }
+
+  // Re-render all pages of the already-loaded document (zoom / resize),
+  // preserving the relative scroll position.
+  async _rerender() {
+    if (!this.doc) return;
+    const generation = ++this.generation;
+
+    for (const rt of this.renderTasks) {
+      try {
+        rt.cancel();
+      } catch { /* ok */ }
+    }
+    this.renderTasks.clear();
+
+    const scrollRatio = this.pagesDiv.scrollHeight > 0
+      ? this.pagesDiv.scrollTop / this.pagesDiv.scrollHeight
+      : 0;
+
+    await this._renderAllPages(this.doc, generation, false);
+    if (generation !== this.generation) return;
+    this.pagesDiv.scrollTop = scrollRatio * this.pagesDiv.scrollHeight;
+  }
+
+  // ---- Loading ----
+
+  async load(url, byteSize) {
+    this.lastUrl = url;
+    this.lastSize = byteSize;
+    this._setState("loading");
+    await this._loadInternal(url, byteSize);
+  }
+
+  async _loadInternal(url, _byteSize) {
+    const generation = ++this.generation;
+    console.log(
+      `[BizMatch] PDF viewer load started: generation ${generation}`,
+    );
+
+    // Await cleanup of previous document (promises may be involved)
+    await this._disposeCurrentDocument();
+    if (generation !== this.generation) return;
+
+    this.pagesDiv.innerHTML = "";
+
+    const loadStart = performance.now();
+    try {
+      const task = pdfjsLib.getDocument({
+        url,
+        rangeChunkSize: 65536,
+        disableAutoFetch: false,
+        // PDF.js >= 5 decodes CCITT-G4/JBIG2 (B/W scans), JPEG2000 and ICC
+        // color via WASM modules fetched from wasmUrl. Without these URLs
+        // the decoders fail silently (ignoreErrors default) and scanned
+        // pages render as blank white canvases of the correct size.
+        wasmUrl: "/pdfjs/wasm/",
+        standardFontDataUrl: "/pdfjs/standard_fonts/",
+        iccUrl: "/pdfjs/iccs/",
+      });
+      this.loadingTask = task;
+
+      const doc = await task.promise;
+      if (generation !== this.generation) {
+        doc.destroy();
+        return;
+      }
+      this.doc = doc;
+      this.numPages = doc.numPages;
+
+      const loadMs = Math.round(performance.now() - loadStart);
+      console.log(
+        `[BizMatch] PDF document loaded: ${this.numPages} pages in ${loadMs}ms`,
+      );
+
+      this.toolbar.hidden = false;
+      this._updateZoomLabel();
+
+      await this._renderAllPages(doc, generation, true);
+      if (generation !== this.generation) return;
+
+      const totalMs = Math.round(performance.now() - loadStart);
+      console.log(
+        `[BizMatch] PDF viewer load completed: generation ${generation}`,
+      );
+      console.log(
+        `[BizMatch] PDF fully rendered: ${this.numPages} pages in ${totalMs}ms`,
+      );
+    } catch (err) {
+      if (generation !== this.generation) return;
+      // Distinguish cancellation from real errors
+      if (isCancellationError(err)) {
+        console.log(
+          `[BizMatch] PDF generation ${generation} cancelled`,
+        );
+        return;
+      }
+      const msg = errorMsg(err);
+      console.error(`[BizMatch] PDF load failed:`, msg);
+      this.errorMsg.textContent = `Unable to open PDF: ${msg}`;
+      this._setState("error");
+    }
+  }
+
+  // Shared render loop for initial load, zoom and resize.
+  // hideLoadingAfterFirstPage: true on initial load (removes the overlay
+  // as soon as page 1 is visible).
+  async _renderAllPages(doc, generation, hideLoadingAfterFirstPage) {
+    this.pagesDiv.innerHTML = "";
+
+    const viewerWidth = this._renderWidth();
+    this._lastRenderWidth = viewerWidth;
+    console.log(`[BizMatch] PDF render width: ${viewerWidth}px`);
+
+    for (let p = 1; p <= this.numPages; p++) {
+      if (generation !== this.generation) return;
+      const pStart = performance.now();
+      await this._renderPage(doc, p, viewerWidth, generation);
+      if (generation !== this.generation) return;
+      if (p === 1 && hideLoadingAfterFirstPage) {
+        this._setState(null); // Remove loading overlay
+      }
+      console.log(
+        `[BizMatch] PDF page ${p} rendered in ${
+          Math.round(performance.now() - pStart)
+        }ms`,
+      );
+      await new Promise((r) => requestAnimationFrame(r));
+    }
+  }
+
+  _setState(state) {
+    this.loadingDiv.hidden = true;
+    this.errorDiv.hidden = true;
+    if (state === "loading") this.loadingDiv.hidden = false;
+    if (state === "error") this.errorDiv.hidden = false;
+    this._viewerState = state;
+  }
+
+  _getViewportWidth() {
+    const style = globalThis.getComputedStyle
+      ? getComputedStyle(this.pagesDiv)
+      : null;
+    let padding = 24; // default guess
+    if (style) {
+      padding = (parseFloat(style.paddingLeft) || 0) +
+        (parseFloat(style.paddingRight) || 0);
+    }
+    const raw = Math.round(this.pagesDiv.clientWidth || 600);
+    return Math.max(raw - padding, 200);
+  }
+
+  async _disposeCurrentDocument() {
+    for (const rt of this.renderTasks) {
+      try {
+        rt.cancel();
+      } catch { /* ok */ }
+    }
+    this.renderTasks.clear();
+
+    if (this.loadingTask) {
+      try {
+        await this.loadingTask.destroy();
+      } catch { /* ok */ }
+      this.loadingTask = null;
+    }
+
+    if (this.doc) {
+      try {
+        await this.doc.destroy();
+      } catch { /* ok */ }
+      this.doc = null;
+      this.numPages = 0;
+    }
+  }
+
+  async _renderPage(doc, pageNum, viewerWidth, generation) {
+    const pageDiv = document.createElement("div");
+    pageDiv.className = "pdf-v-page";
+    pageDiv.dataset.page = String(pageNum);
+    pageDiv.dataset.renderState = "idle";
+
+    const canvas = document.createElement("canvas");
+    pageDiv.appendChild(canvas);
+    this.pagesDiv.appendChild(pageDiv);
+
+    pageDiv.dataset.renderState = "rendering";
+
+    try {
+      const page = await doc.getPage(pageNum);
+      if (generation !== this.generation) return;
+
+      const vp1 = page.getViewport({ scale: 1 });
+      const fitScale = viewerWidth / vp1.width;
+      const viewport = page.getViewport({ scale: fitScale });
+
+      const dpr = Math.min(globalThis.devicePixelRatio || 1, 2);
+      canvas.width = Math.floor(viewport.width * dpr);
+      canvas.height = Math.floor(viewport.height * dpr);
+      canvas.style.width = `${Math.floor(viewport.width)}px`;
+      canvas.style.height = `${Math.floor(viewport.height)}px`;
+
+      const ctx = canvas.getContext("2d");
+      const transform = dpr !== 1 ? [dpr, 0, 0, dpr, 0, 0] : undefined;
+
+      const renderTask = page.render({
+        canvasContext: ctx,
+        viewport,
+        transform,
+      });
+      this.renderTasks.add(renderTask);
+
+      await renderTask.promise;
+      this.renderTasks.delete(renderTask);
+
+      if (generation !== this.generation) return;
+      pageDiv.dataset.renderState = "rendered";
+    } catch (err) {
+      if (generation !== this.generation) return;
+      if (isCancellationError(err)) return;
+      pageDiv.dataset.renderState = "error";
+      console.error(
+        `[BizMatch] Failed to render PDF page ${pageNum}`,
+        err,
+      );
+      if (pageNum === 1) {
+        this.errorMsg.textContent = `Unable to open PDF: ${errorMsg(err)}`;
+        this._setState("error");
+      } else {
+        pageDiv.textContent = `Error rendering page ${pageNum}`;
+        pageDiv.style.padding = "20px";
+        pageDiv.style.color = "#f88";
+        pageDiv.style.textAlign = "center";
+      }
+    }
+  }
+
+  destroy() {
+    this.generation = 0;
+    clearTimeout(this._resizeTimer);
+    clearTimeout(this._zoomTimer);
+    if (this.resizeObserver) {
+      this.resizeObserver.disconnect();
+      this.resizeObserver = null;
+    }
+    this._disposeCurrentDocument().catch(() => {});
+    this.pagesDiv.innerHTML = "";
+    this.toolbar.hidden = true;
+    this._setState("loading");
+  }
+}
+
+function isCancellationError(err) {
+  if (!(err instanceof Error)) return false;
+  const msg = err.message || "";
+  return msg.includes("cancelled") ||
+    msg.includes("canceled") ||
+    msg.includes("destroyed") ||
+    msg.includes("Worker was destroyed");
+}
+
+function errorMsg(err) {
+  return err instanceof Error ? err.message : String(err);
+}
+
+globalThis.PdfViewer = PdfViewer;
\ No newline at end of file
diff --git a/web/public/viewer/viewer.css b/web/public/viewer/viewer.css
new file mode 100644
index 0000000..2830f6e
--- /dev/null
+++ b/web/public/viewer/viewer.css
@@ -0,0 +1,136 @@
+/* Taken from viewer-phase1/styles.css: the .viewer / #pdfViewer rules plus the
+   PDF.js viewer + zoom toolbar blocks. The page is nothing but the viewer pane,
+   so .viewer fills the iframe instead of sitting in a grid column. */
+* {
+  box-sizing: border-box;
+}
+html,
+body {
+  height: 100%;
+}
+body {
+  margin: 0;
+  font: 14px system-ui, sans-serif;
+  color: #202124;
+}
+.viewer {
+  position: relative;
+  height: 100%;
+  background: #555;
+  overflow: hidden;
+}
+.viewer #pdfViewer {
+  position: relative;
+  width: 100%;
+  height: 100%;
+  overflow-y: auto;
+  overflow-x: hidden;
+  background: #525659;
+}
+.viewer #pdfMessage {
+  position: absolute;
+  inset: 0;
+  display: grid;
+  place-items: center;
+  color: white;
+  pointer-events: none;
+  z-index: 2;
+  white-space: pre-wrap;
+  padding: 20px;
+  text-align: center;
+}
+.viewer.loaded #pdfMessage {
+  display: none;
+}
+
+/* PDF.js viewer */
+.pdf-v-overlay {
+  position: absolute;
+  inset: 0;
+  z-index: 1;
+}
+.pdf-v-loading {
+  padding: 40px 20px;
+  color: #aaa;
+  text-align: center;
+  font-size: 15px;
+}
+.pdf-v-error {
+  padding: 30px 20px;
+  text-align: center;
+}
+.pdf-v-error-msg {
+  color: #f88;
+  font-size: 16px;
+  margin-bottom: 12px;
+  white-space: pre-wrap;
+}
+.pdf-v-retry {
+  padding: 8px 24px;
+  font-size: 14px;
+  cursor: pointer;
+  border: 1px solid #888;
+  background: #444;
+  color: #eee;
+  border-radius: 4px;
+}
+.pdf-v-retry:hover {
+  background: #555;
+}
+.pdf-v-pages {
+  box-sizing: border-box;
+  width: 100%;
+  height: 100%;
+  overflow-y: scroll;
+  overflow-x: auto;
+  scrollbar-gutter: stable;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  align-items: safe center; /* keeps left edge reachable when zoomed wider than the pane */
+  gap: 16px;
+  padding: 12px;
+}
+.pdf-v-page {
+  background: white;
+  box-shadow: 0 1px 5px rgba(0, 0, 0, 0.35);
+  flex-shrink: 0;
+}
+.pdf-v-page canvas {
+  display: block;
+}
+
+/* Zoom toolbar */
+.pdf-v-toolbar {
+  position: absolute;
+  top: 10px;
+  right: 24px;
+  z-index: 3;
+  display: flex;
+  align-items: center;
+  gap: 2px;
+  background: rgba(35, 35, 38, 0.88);
+  border: 1px solid #666;
+  border-radius: 6px;
+  padding: 3px 4px;
+  box-shadow: 0 1px 5px rgba(0, 0, 0, 0.4);
+}
+.pdf-v-toolbar button {
+  border: 0;
+  background: transparent;
+  color: #e5e5e5;
+  font-size: 15px;
+  line-height: 1;
+  padding: 5px 9px;
+  cursor: pointer;
+  border-radius: 4px;
+}
+.pdf-v-toolbar button:hover {
+  background: #555;
+}
+.pdf-v-zoom-label {
+  min-width: 52px;
+  text-align: center;
+  font-size: 12px !important;
+  color: #ccc !important;
+}
diff --git a/web/public/viewer/viewer.js b/web/public/viewer/viewer.js
new file mode 100644
index 0000000..ec7041b
--- /dev/null
+++ b/web/public/viewer/viewer.js
@@ -0,0 +1,51 @@
+// Bootstrap for the standalone PDF viewer page. Plays the role of app.js in
+// viewer-phase1: it owns the #pdfMessage overlay and hands one URL to PdfViewer
+// (from pdf_viewer.js, unchanged). Everything else — zoom, resize, retry — lives
+// in PdfViewer already.
+//
+// URL contract:  /viewer/index.html?file=<urlencoded /api/... path>
+// Same-origin only: any file value that is not a root-relative /api/ path is
+// refused before it ever reaches pdf.js.
+
+const viewer = document.querySelector(".viewer");
+const pdfContainer = document.querySelector("#pdfViewer");
+const pdfMessage = document.querySelector("#pdfMessage");
+
+function showMessage(text) {
+  viewer.classList.remove("loaded");
+  pdfMessage.textContent = text;
+  pdfMessage.hidden = false;
+}
+
+// Only root-relative /api/ paths. Rejects absolute URLs ("https://..."),
+// protocol-relative ones ("//host/api/x") and anything outside /api/.
+function safeFileUrl(raw) {
+  if (!raw) return null;
+  if (!raw.startsWith("/api/") || raw.startsWith("//")) return null;
+  // A backslash can be normalized to "/" by some URL parsers — reject outright.
+  if (raw.includes("\\")) return null;
+  return raw;
+}
+
+const params = new URLSearchParams(globalThis.location.search);
+const file = safeFileUrl(params.get("file"));
+
+if (!file) {
+  showMessage(
+    params.get("file")
+      ? "Refused to load this document: only same-origin /api/ paths are allowed."
+      : "Select a document",
+  );
+} else {
+  showMessage("Loading PDF…");
+  const pdfViewer = new PdfViewer(pdfContainer);
+  viewer.classList.add("loaded");
+  pdfMessage.hidden = true;
+  pdfViewer.load(file).catch((error) => {
+    showMessage(
+      `Cannot open PDF: ${
+        error instanceof Error ? error.message : String(error)
+      }`,
+    );
+  });
+}
diff --git a/web/scripts/copy-pdfjs.mjs b/web/scripts/copy-pdfjs.mjs
new file mode 100644
index 0000000..5a55c3e
--- /dev/null
+++ b/web/scripts/copy-pdfjs.mjs
@@ -0,0 +1,39 @@
+// Copies the pdf.js runtime assets out of node_modules into public/pdfjs/ so the
+// standalone viewer (public/viewer/) can load them as plain, unbundled ES modules.
+// Runs via predev/prebuild, i.e. also inside the Docker web build stage.
+//
+// The target layout is dictated by the URLs the ported viewer uses:
+//   /pdfjs/legacy/pdf.min.mjs         (import + GlobalWorkerOptions.workerSrc)
+//   /pdfjs/wasm/                      (wasmUrl  — CCITT-G4/JBIG2, JPEG2000, ICC decoders)
+//   /pdfjs/standard_fonts/            (standardFontDataUrl)
+//   /pdfjs/iccs/                      (iccUrl)
+import { cp, mkdir, rm, stat } from 'node:fs/promises';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const webRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
+const src = path.join(webRoot, 'node_modules', 'pdfjs-dist');
+const dest = path.join(webRoot, 'public', 'pdfjs');
+
+try {
+  await stat(src);
+} catch {
+  console.error(`[copy-pdfjs] ${src} not found — run npm install first.`);
+  process.exit(1);
+}
+
+// Full rebuild, so a pdfjs-dist upgrade never leaves stale files behind.
+await rm(dest, { recursive: true, force: true });
+await mkdir(path.join(dest, 'legacy'), { recursive: true });
+
+const files = ['pdf.min.mjs', 'pdf.worker.min.mjs'];
+for (const file of files) {
+  await cp(path.join(src, 'legacy', 'build', file), path.join(dest, 'legacy', file));
+}
+
+const dirs = ['wasm', 'standard_fonts', 'iccs'];
+for (const dir of dirs) {
+  await cp(path.join(src, dir), path.join(dest, dir), { recursive: true });
+}
+
+console.log(`[copy-pdfjs] ${files.join(', ')} + ${dirs.join('/, ')}/ -> public/pdfjs/`);
diff --git a/web/src/App.tsx b/web/src/App.tsx
index 45377b9..989a437 100644
--- a/web/src/App.tsx
+++ b/web/src/App.tsx
@@ -31,8 +31,10 @@ export default function App() {
   if (!staff) return <Login onLogin={setStaff} />;
 
   return (
-    <div className="min-h-screen bg-gray-50 text-gray-900">
-      <header className="flex items-center justify-between border-b border-gray-200 bg-white px-6 py-3">
+    // h-screen + min-h-0 below, so the business detail's master-detail split can
+    // fill exactly the remaining viewport height.
+    <div className="flex h-screen flex-col bg-gray-50 text-gray-900">
+      <header className="flex shrink-0 items-center justify-between border-b border-gray-200 bg-white px-6 py-3">
         <button
           className="text-base font-semibold tracking-tight"
           onClick={() => setView({ name: 'businesses' })}
@@ -50,13 +52,15 @@ export default function App() {
         </div>
       </header>
 
-      <main className="mx-auto max-w-5xl px-6 py-6">
-        {view.name === 'businesses' ? (
+      {view.name === 'businesses' ? (
+        <main className="mx-auto w-full max-w-5xl flex-1 overflow-auto px-6 py-6">
           <Businesses onOpen={(id) => setView({ name: 'business', id })} />
-        ) : (
+        </main>
+      ) : (
+        <main className="flex min-h-0 flex-1 flex-col px-6 py-4">
           <BusinessDetail id={view.id} onBack={() => setView({ name: 'businesses' })} />
-        )}
-      </main>
+        </main>
+      )}
     </div>
   );
 }
diff --git a/web/src/api.ts b/web/src/api.ts
index 06af8f2..65fa3c3 100644
--- a/web/src/api.ts
+++ b/web/src/api.ts
@@ -25,7 +25,8 @@ export interface Business {
 }
 
 export interface BusinessFile {
-  name: string;
+  /** Relative to the business directory, posix separators. */
+  path: string;
   size: number;
   mtime: string;
 }
@@ -73,3 +74,13 @@ export const api = {
   businessFiles: (id: string) => request<BusinessFile[]>(`/api/businesses/${id}/files`),
   scan: () => post<ScanResult>('/api/businesses/scan'),
 };
+
+/** Same-origin streaming URL of one file inside a business directory. */
+export function businessFileUrl(id: string, filePath: string): string {
+  return `/api/businesses/${id}/file?path=${encodeURIComponent(filePath)}`;
+}
+
+/** The standalone (unbundled) pdf.js viewer page, pointed at a business file. */
+export function viewerUrl(id: string, filePath: string): string {
+  return `/viewer/index.html?file=${encodeURIComponent(businessFileUrl(id, filePath))}`;
+}
diff --git a/web/src/views/BusinessDetail.tsx b/web/src/views/BusinessDetail.tsx
index 9d1f99a..c48c68e 100644
--- a/web/src/views/BusinessDetail.tsx
+++ b/web/src/views/BusinessDetail.tsx
@@ -1,5 +1,11 @@
 import { useEffect, useState } from 'react';
-import { api, type Business, type BusinessFile } from '../api.js';
+import {
+  api,
+  businessFileUrl,
+  viewerUrl,
+  type Business,
+  type BusinessFile,
+} from '../api.js';
 
 function formatSize(bytes: number): string {
   if (bytes >= 1024 * 1024) return `${(bytes / 1024 / 1024).toFixed(1)} MB`;
@@ -16,61 +22,108 @@ function formatDate(iso: string): string {
   });
 }
 
+const isPdf = (filePath: string) => filePath.toLowerCase().endsWith('.pdf');
+
 export default function BusinessDetail({ id, onBack }: { id: string; onBack: () => void }) {
   const [business, setBusiness] = useState<Business | null>(null);
   const [files, setFiles] = useState<BusinessFile[] | null>(null);
   const [error, setError] = useState<string | null>(null);
+  const [selected, setSelected] = useState<string | null>(null);
 
   useEffect(() => {
+    setSelected(null);
     api.business(id).then(setBusiness).catch((err: Error) => setError(err.message));
     api.businessFiles(id).then(setFiles).catch((err: Error) => setError(err.message));
   }, [id]);
 
   return (
-    <div>
-      <button onClick={onBack} className="mb-4 text-sm text-blue-600 hover:underline">
-        ← Back to businesses
-      </button>
+    <div className="flex h-full min-h-0 flex-col">
+      <div className="mb-3 shrink-0">
+        <button onClick={onBack} className="text-sm text-blue-600 hover:underline">
+          ← Back to businesses
+        </button>
 
-      {error && <p className="mb-3 text-sm text-red-600">{error}</p>}
+        {error && <p className="mt-2 text-sm text-red-600">{error}</p>}
 
-      {business && (
-        <div className="mb-5">
-          <div className="flex items-center gap-3">
-            <h1 className="text-lg font-semibold">{business.name}</h1>
-            <span className="rounded-full border border-gray-300 bg-white px-2 py-0.5 text-xs text-gray-600">
-              {business.status}
-            </span>
+        {business && (
+          <div className="mt-2">
+            <div className="flex items-center gap-3">
+              <h1 className="text-lg font-semibold">{business.name}</h1>
+              <span className="rounded-full border border-gray-300 bg-white px-2 py-0.5 text-xs text-gray-600">
+                {business.status}
+              </span>
+            </div>
+            <p className="mt-1 font-mono text-xs text-gray-500">{business.nas_path}</p>
           </div>
-          <p className="mt-1 font-mono text-xs text-gray-500">{business.nas_path}</p>
-        </div>
-      )}
+        )}
+      </div>
 
-      <table className="w-full border-collapse bg-white text-sm">
-        <thead>
-          <tr className="border-b border-gray-200 text-left text-xs uppercase tracking-wide text-gray-500">
-            <th className="px-3 py-2 font-medium">File</th>
-            <th className="w-24 px-3 py-2 font-medium">Size</th>
-            <th className="w-48 px-3 py-2 font-medium">Modified</th>
-          </tr>
-        </thead>
-        <tbody>
-          {files?.map((f) => (
-            <tr key={f.name} className="border-b border-gray-100">
-              <td className="px-3 py-1.5">{f.name}</td>
-              <td className="px-3 py-1.5 text-gray-500">{formatSize(f.size)}</td>
-              <td className="px-3 py-1.5 text-gray-500">{formatDate(f.mtime)}</td>
-            </tr>
-          ))}
-          {files && files.length === 0 && (
-            <tr>
-              <td colSpan={3} className="px-3 py-4 text-gray-500">
-                No files in this directory.
-              </td>
-            </tr>
+      {/* Master-detail: file table left, PDF viewer right, together filling the viewport. */}
+      <div className="flex min-h-0 flex-1 gap-4">
+        <div className="min-w-0 flex-1 overflow-auto rounded border border-gray-200 bg-white">
+          <table className="w-full border-collapse text-sm">
+            <thead className="sticky top-0 bg-white">
+              <tr className="border-b border-gray-200 text-left text-xs uppercase tracking-wide text-gray-500">
+                <th className="px-3 py-2 font-medium">File</th>
+                <th className="w-24 px-3 py-2 font-medium">Size</th>
+                <th className="w-44 px-3 py-2 font-medium">Modified</th>
+              </tr>
+            </thead>
+            <tbody>
+              {files?.map((f) => (
+                <tr
+                  key={f.path}
+                  onClick={isPdf(f.path) ? () => setSelected(f.path) : undefined}
+                  className={`border-b border-gray-100 ${
+                    isPdf(f.path) ? 'cursor-pointer hover:bg-gray-50' : ''
+                  } ${f.path === selected ? 'bg-blue-50 hover:bg-blue-50' : ''}`}
+                >
+                  <td className="px-3 py-1.5">
+                    {isPdf(f.path) ? (
+                      <span className={f.path === selected ? 'font-medium text-blue-700' : ''}>
+                        {f.path}
+                      </span>
+                    ) : (
+                      <a
+                        href={businessFileUrl(id, f.path)}
+                        className="text-blue-600 hover:underline"
+                      >
+                        {f.path}
+                      </a>
+                    )}
+                  </td>
+                  <td className="px-3 py-1.5 text-gray-500">{formatSize(f.size)}</td>
+                  <td className="px-3 py-1.5 text-gray-500">{formatDate(f.mtime)}</td>
+                </tr>
+              ))}
+              {files && files.length === 0 && (
+                <tr>
+                  <td colSpan={3} className="px-3 py-4 text-gray-500">
+                    No files in this directory.
+                  </td>
+                </tr>
+              )}
+            </tbody>
+          </table>
+        </div>
+
+        <div className="min-w-0 flex-1 overflow-hidden rounded border border-gray-200 bg-gray-100">
+          {selected ? (
+            <iframe
+              // Remounting on `key` change is what makes the standalone page reload
+              // the new document — it reads ?file= once at startup.
+              key={selected}
+              src={viewerUrl(id, selected)}
+              title={selected}
+              className="h-full w-full border-0"
+            />
+          ) : (
+            <div className="flex h-full items-center justify-center text-sm text-gray-500">
+              Select a PDF to view it here.
+            </div>
           )}
-        </tbody>
-      </table>
+        </div>
+      </div>
     </div>
   );
 }