diff --git a/apps/web/src/components/PdfViewer.test.tsx b/apps/web/src/components/PdfViewer.test.tsx
index 29abb2b..ae6af51 100644
--- a/apps/web/src/components/PdfViewer.test.tsx
+++ b/apps/web/src/components/PdfViewer.test.tsx
@@ -1,4 +1,4 @@
-import { act, cleanup, render, screen, waitFor } from '@testing-library/react';
+import { act, cleanup, fireEvent, render, screen, waitFor } from '@testing-library/react';
 import { afterEach, beforeEach, expect, it, vi } from 'vitest';
 import type { ApiClient } from '../lib/api';
 import { PdfViewer } from './PdfViewer';
@@ -12,8 +12,8 @@ function deferred<T>() {
   const promise = new Promise<T>((done, fail) => { resolve = done; reject = fail; });
   return { promise, resolve, reject };
 }
-function document() {
-  return { numPages: 1, getPage: vi.fn(async () => ({ getViewport: () => ({ width: 200, height: 300 }) })) };
+function document(numPages = 1) {
+  return { numPages, getPage: vi.fn(async () => ({ getViewport: ({ scale }: { scale: number }) => ({ width: 200 * scale, height: 300 * scale }) })) };
 }
 function properties(data = new ArrayBuffer(1)) {
   return {
@@ -24,6 +24,7 @@ function properties(data = new ArrayBuffer(1)) {
 }
 beforeEach(() => {
   vi.resetAllMocks();
+  window.localStorage.clear();
   vi.spyOn(HTMLCanvasElement.prototype, 'getContext').mockReturnValue(null);
   vi.stubGlobal('requestAnimationFrame', (callback: FrameRequestCallback) => { callback(0); return 1; });
 });
@@ -59,6 +60,142 @@ it('does not report a cancelled old parser failure against replacement bytes', a
   expect(screen.queryByText('Old PDF was invalid')).not.toBeInTheDocument();
 });
 
+async function gestureViewer(focusMode = true, numPages = 1) {
+  parser.getDocument.mockImplementation(() => ({ promise: Promise.resolve(document(numPages)), destroy: vi.fn() }));
+  const props = properties();
+  const view = render(<PdfViewer {...props} focusMode={focusMode}/>);
+  // The callback runs before React commits rendering=false and installs touch listeners.
+  await act(async () => {
+    await waitFor(() => expect(props.onDocumentStatus).toHaveBeenCalledWith(props.data, 'ready'));
+  });
+  const root = view.container.querySelector<HTMLDivElement>('.pdf-scroll')!;
+  const page = screen.getByLabelText('PDF page 1');
+  vi.spyOn(root, 'getBoundingClientRect').mockReturnValue({ left: 10, top: 20 } as DOMRect);
+  [...view.container.querySelectorAll<HTMLElement>('.pdf-page')].forEach((element, index, elements) => {
+    Object.defineProperties(element, {
+      offsetLeft: { get: () => 16 },
+      offsetTop: { get: () => 35 + elements.slice(0, index).reduce((top, previous) => top + parseFloat(previous.style.height) + 18, 0) },
+      offsetHeight: { get: () => parseFloat(element.style.height) }
+    });
+  });
+  root.scrollLeft = 60;
+  root.scrollTop = 90;
+  return { ...view, root, page, props };
+}
+const fingers = (left: number, right: number, y = 170) => [
+  { identifier: 1, clientX: left, clientY: y }, { identifier: 2, clientX: right, clientY: y }
+];
+
+it('previews a fullscreen pinch at its moving midpoint and renders sharp pages only on release', async () => {
+  const { root, page } = await gestureViewer();
+  expect(fireEvent.touchStart(root, { touches: fingers(60, 160) })).toBe(false);
+  fireEvent.touchMove(root, { touches: fingers(30, 230, 200) });
+  expect(page.style.width).toBe('400px');
+  expect(page.querySelector('canvas')!.style.height).toBe('600px');
+  expect(root.scrollLeft).toBe(184);
+  expect(root.scrollTop).toBe(265);
+  expect(parser.getDocument).toHaveBeenCalledTimes(1);
+  fireEvent.touchEnd(root, { touches: [] });
+  await waitFor(() => expect(screen.getByText('200%')).toBeInTheDocument());
+  await waitFor(() => expect(parser.getDocument).toHaveBeenCalledTimes(2));
+  expect(screen.getByLabelText('PDF page 1').style.width).toBe('400px');
+  expect(root.scrollLeft).toBe(184);
+  expect(root.scrollTop).toBe(265);
+  expect(JSON.parse(window.localStorage.getItem('overroot.pdfView.pdf-validation-test')!)).toMatchObject({ zoom: 2, scrollLeft: 184, scrollTop: 265 });
+});
+
+it('keeps a later page under the fingers as preceding pages grow', async () => {
+  const { root } = await gestureViewer(true, 2);
+  root.scrollTop = 400;
+  fireEvent.touchStart(root, { touches: fingers(60, 160) });
+  fireEvent.touchMove(root, { touches: fingers(10, 210) });
+  expect(root.scrollTop).toBe(897);
+  fireEvent.touchEnd(root, { touches: [] });
+  await waitFor(() => expect(parser.getDocument).toHaveBeenCalledTimes(2));
+  expect(root.scrollTop).toBe(897);
+  expect(screen.getByLabelText('PDF page 2').style.height).toBe('600px');
+});
+
+it('commits the preview when leaving fullscreen during a pinch', async () => {
+  const { root, props, rerender } = await gestureViewer();
+  fireEvent.touchStart(root, { touches: fingers(60, 160) });
+  fireEvent.touchMove(root, { touches: fingers(10, 210) });
+  expect(screen.getByLabelText('PDF page 1').style.width).toBe('400px');
+  rerender(<PdfViewer {...props} focusMode={false}/>);
+  await screen.findByText('200%');
+  await waitFor(() => expect(parser.getDocument).toHaveBeenCalledTimes(2));
+  expect(screen.getByLabelText('PDF page 1').style.width).toBe('400px');
+  expect(fireEvent.touchStart(root, { touches: fingers(60, 160) })).toBe(true);
+});
+
+it.each([
+  { left: -140, right: 360, width: '500px', readout: '250%' },
+  { left: 105, right: 115, width: '100px', readout: '50%' }
+])('clamps pinch zoom to $readout and commits on cancellation', async ({ left, right, width, readout }) => {
+  const { root, page } = await gestureViewer();
+  fireEvent.touchStart(root, { touches: fingers(60, 160) });
+  fireEvent.touchMove(root, { touches: fingers(left, right) });
+  expect(page.style.width).toBe(width);
+  fireEvent.touchCancel(root, { touches: [] });
+  await screen.findByText(readout);
+  await waitFor(() => expect(parser.getDocument).toHaveBeenCalledTimes(2));
+});
+
+it('ends a pinch when a third finger joins and ignores a replacement pair', async () => {
+  const { root } = await gestureViewer();
+  fireEvent.touchStart(root, { touches: fingers(60, 160) });
+  fireEvent.touchMove(root, { touches: fingers(10, 210) });
+  const third = { identifier: 3, clientX: 300, clientY: 170 };
+  fireEvent.touchStart(root, { touches: [...fingers(10, 210), third] });
+  const replacement = [fingers(10, 210)[1]!, third];
+  fireEvent.touchEnd(root, { touches: replacement });
+  fireEvent.touchMove(root, { touches: [replacement[0]!, { ...third, clientX: 500 }] });
+  await screen.findByText('200%');
+  await waitFor(() => expect(parser.getDocument).toHaveBeenCalledTimes(2));
+  expect(screen.getByLabelText('PDF page 1').style.width).toBe('400px');
+});
+
+it.each(['touchEnd', 'touchMove', 'touchCancel'] as const)('ends the active pinch on %s with a changed or cancelled pair', async (event) => {
+  const { root } = await gestureViewer();
+  fireEvent.touchStart(root, { touches: fingers(60, 160) });
+  fireEvent.touchMove(root, { touches: fingers(10, 210) });
+  const remaining = fingers(10, 210);
+  if (event !== 'touchCancel') remaining[1]!.identifier = 3;
+  fireEvent[event](root, { touches: remaining });
+  await screen.findByText('200%');
+  await waitFor(() => expect(parser.getDocument).toHaveBeenCalledTimes(2));
+  fireEvent.touchMove(root, { touches: fingers(-100, 300) });
+  expect(screen.getByLabelText('PDF page 1').style.width).toBe('400px');
+  expect(parser.getDocument).toHaveBeenCalledTimes(2);
+});
+
+it('accepts reordered touches belonging to the same active pair', async () => {
+  const { root, page } = await gestureViewer();
+  fireEvent.touchStart(root, { touches: fingers(60, 160) });
+  fireEvent.touchMove(root, { touches: fingers(10, 210).reverse() });
+  expect(page.style.width).toBe('400px');
+  fireEvent.touchEnd(root, { touches: [] });
+  await screen.findByText('200%');
+});
+
+it('leaves ordinary one-finger scrolling to the browser', async () => {
+  const { root, page } = await gestureViewer();
+  expect(fireEvent.touchStart(root, { touches: fingers(60, 160).slice(0, 1) })).toBe(true);
+  expect(fireEvent.touchMove(root, { touches: fingers(80, 180).slice(0, 1) })).toBe(true);
+  fireEvent.scroll(root, { target: { scrollLeft: 100, scrollTop: 150 } });
+  expect(page.style.width).toBe('200px');
+  expect(parser.getDocument).toHaveBeenCalledTimes(1);
+});
+
+it('does not intercept pinches outside fullscreen', async () => {
+  const { root, page } = await gestureViewer(false);
+  expect(fireEvent.touchStart(root, { touches: fingers(60, 160) })).toBe(true);
+  expect(fireEvent.touchMove(root, { touches: fingers(10, 210) })).toBe(true);
+  fireEvent.touchEnd(root, { touches: [] });
+  expect(page.style.width).toBe('200px');
+  expect(parser.getDocument).toHaveBeenCalledTimes(1);
+});
+
 it('uses the latest validation callback without restarting a pending document', async () => {
   const pending = deferred<ReturnType<typeof document>>();
   parser.getDocument.mockReturnValue({ promise: pending.promise, destroy: vi.fn() });
diff --git a/apps/web/src/components/PdfViewer.tsx b/apps/web/src/components/PdfViewer.tsx
index 8c7f58e..4023308 100644
--- a/apps/web/src/components/PdfViewer.tsx
+++ b/apps/web/src/components/PdfViewer.tsx
@@ -160,6 +160,98 @@ export function PdfViewer({
     };
   }, [projectHash]);
 
+  useEffect(() => {
+    const root = scroller.current;
+    const content = pages.current;
+    if (!focusMode || rendering || !pageCount || !root || !content) return;
+
+    type Pinch = {
+      distance: number; zoom: number; nextZoom: number; ids: [number, number];
+      anchor: HTMLElement; x: number; y: number;
+      sizes: { element: HTMLElement; width: number; height: number }[];
+    };
+    let pinch: Pinch | null = null;
+    const midpoint = (touches: TouchList) => {
+      const bounds = root.getBoundingClientRect();
+      return {
+        x: (touches[0]!.clientX + touches[1]!.clientX) / 2 - bounds.left,
+        y: (touches[0]!.clientY + touches[1]!.clientY) / 2 - bounds.top
+      };
+    };
+    const distance = (touches: TouchList) => Math.hypot(
+      touches[0]!.clientX - touches[1]!.clientX, touches[0]!.clientY - touches[1]!.clientY
+    );
+    const finish = () => {
+      if (!pinch) return;
+      const next = pinch.nextZoom;
+      pinch = null;
+      zoomRef.current = next;
+      canPersist.current = true;
+      setZoom(next);
+      persistViewState();
+    };
+    const samePair = (touches: TouchList) => pinch && touches.length === 2 &&
+      [...touches].every((touch) => pinch!.ids.includes(touch.identifier));
+    const start = (event: TouchEvent) => {
+      if (pinch) {
+        if (!samePair(event.touches)) finish();
+        return;
+      }
+      if (event.touches.length !== 2) return;
+      const span = distance(event.touches);
+      if (!span) return;
+      const point = midpoint(event.touches);
+      const elements = [...content.querySelectorAll<HTMLElement>('.pdf-page')];
+      const anchor = elements.find((element) => element.offsetTop + element.offsetHeight > root.scrollTop + point.y) ?? elements.at(-1);
+      if (!anchor) return;
+      event.preventDefault();
+      const currentZoom = zoomRef.current;
+      pinch = {
+        distance: span, zoom: currentZoom, nextZoom: currentZoom, anchor,
+        ids: [event.touches[0]!.identifier, event.touches[1]!.identifier],
+        x: (root.scrollLeft + point.x - anchor.offsetLeft) / currentZoom,
+        y: (root.scrollTop + point.y - anchor.offsetTop) / currentZoom,
+        sizes: elements.map((element) => ({ element, width: parseFloat(element.style.width), height: parseFloat(element.style.height) }))
+      };
+      canPersist.current = false;
+    };
+    const move = (event: TouchEvent) => {
+      if (!samePair(event.touches)) {
+        finish();
+        return;
+      }
+      if (pinch) {
+        event.preventDefault();
+        const point = midpoint(event.touches);
+        const next = Math.min(2.5, Math.max(0.5, pinch.zoom * distance(event.touches) / pinch.distance));
+        // Resize the existing canvases for a smooth preview; render sharp pixels only on release.
+        for (const { element, width, height } of pinch.sizes) {
+          const canvas = element.querySelector('canvas')!;
+          element.style.width = canvas.style.width = `${width * next / pinch.zoom}px`;
+          element.style.height = canvas.style.height = `${height * next / pinch.zoom}px`;
+        }
+        root.scrollLeft = pinch.anchor.offsetLeft + pinch.x * next - point.x;
+        root.scrollTop = pinch.anchor.offsetTop + pinch.y * next - point.y;
+        pinch.nextZoom = next;
+        paintPdfHighlights(content, sourceHighlights, next);
+      }
+    };
+    const end = (event: TouchEvent) => {
+      if (!samePair(event.touches)) finish();
+    };
+    root.addEventListener('touchstart', start, { passive: false });
+    root.addEventListener('touchmove', move, { passive: false });
+    root.addEventListener('touchend', end);
+    root.addEventListener('touchcancel', finish);
+    return () => {
+      root.removeEventListener('touchstart', start);
+      root.removeEventListener('touchmove', move);
+      root.removeEventListener('touchend', end);
+      root.removeEventListener('touchcancel', finish);
+      finish();
+    };
+  }, [focusMode, rendering, pageCount, sourceHighlights]);
+
   function visiblePage() {
     const root = scroller.current;
     if (!root) return 1;
diff --git a/apps/web/src/styles.css b/apps/web/src/styles.css
index 1f0b632..a155ab0 100644
--- a/apps/web/src/styles.css
+++ b/apps/web/src/styles.css
@@ -346,6 +346,7 @@ button:disabled { cursor: default; opacity: .42; }
 .pdf-viewer--focus { position: fixed; z-index: 100; inset: 0; width: 100vw; height: 100dvh; grid-template-rows: 0 minmax(0, 1fr); }
 .workspace-shell--pdf-focus .pdf-wrap { container-type: normal; overflow: visible; }
 .pdf-viewer--focus .pdf-toolbar { visibility: hidden; }
+.pdf-viewer--focus .pdf-scroll { touch-action: pan-x pan-y; }
 .pdf-viewer--focus .pdf-pages { padding-top: 35px; }
 
 @container (max-width: 400px) {