diff --git a/main.ts b/main.ts
index ef50d57..2b9125f 100644
--- a/main.ts
+++ b/main.ts
@@ -765,4 +765,29 @@ try {
   );
 }
 
-win.show();
\ No newline at end of file
+win.show();
+
+// Workaround: with the experimental desktop backend the first BrowserWindow
+// "adopts" the implicit startup window, which is created before user code
+// runs. Sometimes the native window keeps its built-in default size even
+// though getSize() already reports the requested values, so the early
+// setSize-on-mismatch above is skipped. Enforce the persisted size
+// unconditionally after show(), and verify once more shortly after.
+try {
+  win.setSize(clamped.windowWidth, clamped.windowHeight);
+  setTimeout(() => {
+    try {
+      const [w, h] = win.getSize();
+      if (w !== clamped.windowWidth || h !== clamped.windowHeight) {
+        console.log(
+          `${PREFIX} Window size drifted to ${w}x${h}, enforcing ${clamped.windowWidth}x${clamped.windowHeight}`,
+        );
+        win.setSize(clamped.windowWidth, clamped.windowHeight);
+      }
+    } catch { /* ok */ }
+  }, 250);
+} catch (err) {
+  console.warn(
+    `${PREFIX} Post-show size enforcement failed: ${errorMessage(err)}`,
+  );
+}
\ No newline at end of file
diff --git a/web/pdf_viewer.js b/web/pdf_viewer.js
index 224f930..2f369f2 100644
--- a/web/pdf_viewer.js
+++ b/web/pdf_viewer.js
@@ -1,22 +1,38 @@
 // 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) {
     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;
+    this.zoom = 1; // multiplier on fit-to-width (1 = fit width)
+    this._lastRenderWidth = 0;
+    this._resizeTimer = null;
+    this._zoomTimer = null;
+    this.resizeObserver = null;
     this._createDOM();
+    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="Verkleinern (Strg+Mausrad)">\u2212</button>
+        <button class="pdf-v-zoom-label" title="Auf Seitenbreite einpassen">100%</button>
+        <button class="pdf-v-zoom-in" title="Vergr\u00f6\u00dfern (Strg+Mausrad)">+</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>
@@ -24,6 +40,8 @@ class PdfViewer {
         <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");
@@ -36,16 +54,90 @@ class PdfViewer {
         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 });
   }
 
-  _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;
+  // ---- 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 QC] 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;
@@ -87,50 +179,25 @@ class PdfViewer {
         return;
       }
       this.doc = doc;
+      this.numPages = doc.numPages;
 
-      const numPages = doc.numPages;
       const loadMs = Math.round(performance.now() - loadStart);
       console.log(
-        `[BizMatch QC] PDF document loaded: ${numPages} pages in ${loadMs}ms`,
+        `[BizMatch QC] PDF document loaded: ${this.numPages} pages in ${loadMs}ms`,
       );
 
-      const viewerWidth = this._getViewportWidth();
-      console.log(`[BizMatch QC] PDF usable render width: ${viewerWidth}px`);
+      this.toolbar.hidden = false;
+      this._updateZoomLabel();
 
-      const pageStart = performance.now();
-      await this._renderPage(doc, 1, viewerWidth, generation);
+      await this._renderAllPages(doc, generation, true);
       if (generation !== this.generation) return;
 
-      this._setState(null); // Remove loading overlay
-      const firstPageMs = Math.round(performance.now() - pageStart);
-      console.log(
-        `[BizMatch QC] PDF page 1 rendered in ${firstPageMs}ms`,
-      );
-      console.log(
-        `[BizMatch QC] First page visible after ${
-          Math.round(performance.now() - loadStart)
-        }ms`,
-      );
-
-      for (let p = 2; p <= numPages; p++) {
-        if (generation !== this.generation) return;
-        const pStart = performance.now();
-        await this._renderPage(doc, p, viewerWidth, generation);
-        if (generation !== this.generation) return;
-        console.log(
-          `[BizMatch QC] PDF page ${p} rendered in ${
-            Math.round(performance.now() - pStart)
-          }ms`,
-        );
-        await new Promise((r) => requestAnimationFrame(r));
-      }
-
       const totalMs = Math.round(performance.now() - loadStart);
       console.log(
         `[BizMatch QC] PDF viewer load completed: generation ${generation}`,
       );
       console.log(
-        `[BizMatch QC] PDF fully rendered: ${numPages} pages in ${totalMs}ms`,
+        `[BizMatch QC] PDF fully rendered: ${this.numPages} pages in ${totalMs}ms`,
       );
     } catch (err) {
       if (generation !== this.generation) return;
@@ -148,6 +215,41 @@ class PdfViewer {
     }
   }
 
+  // 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 QC] 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 QC] 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)
@@ -181,6 +283,7 @@ class PdfViewer {
         await this.doc.destroy();
       } catch { /* ok */ }
       this.doc = null;
+      this.numPages = 0;
     }
   }
 
@@ -247,8 +350,15 @@ class PdfViewer {
 
   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");
   }
 }
@@ -257,7 +367,7 @@ function isCancellationError(err) {
   if (!(err instanceof Error)) return false;
   const msg = err.message || "";
   return msg.includes("cancelled") ||
-    msg.includes("cancelled") ||
+    msg.includes("canceled") ||
     msg.includes("destroyed") ||
     msg.includes("Worker was destroyed");
 }
diff --git a/web/styles.css b/web/styles.css
index db4edc5..69a2b87 100644
--- a/web/styles.css
+++ b/web/styles.css
@@ -229,11 +229,12 @@ hr.field-sep {
   width: 100%;
   height: 100%;
   overflow-y: scroll;
-  overflow-x: hidden;
+  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;
 }
@@ -245,3 +246,38 @@ hr.field-sep {
 .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;
+}
\ No newline at end of file