PDF Compare (Visual/Text Diff) — Heatmap, Text Diff, and Two-Up Export
Quickly spot differences between two PDF files—visually and by text—without uploading your documents. Our PDF Compare tool renders pages locally, overlays a pixel-diff heatmap, and provides a side-by-side text diff. Enjoy synchronized zoom and scrolling, page thumbnails for fast navigation, and one-click two-up diff PDF exports.
Key Features
Visual Pixel Diff
Overlay a heatmap to highlight where pages differ. Choose Heatmap, Binary, or Pixelmatch modes; tune threshold and opacity for clarity.
Text Diff
Compare extracted text per page or entire document with clear <ins>
/<del>
highlights to reveal wording changes.
Synchronized Zoom & Scroll
Zoom both PDFs and the heatmap together (slider, +/−, or Ctrl/Cmd+wheel) and keep viewers in lockstep while panning.
Thumbnails Navigation
Per-page thumbnails for A and B let you jump directly to any page pair. Designed mobile-first for quick review on the go.
Smart Noise Controls
Denoise blur, Ignore Anti-aliasing, and optional Edge-Weighted mode reduce rendering speckle and emphasize structural changes.
Two-Up Diff PDF Export
Export A|B, A|Diff, or A|Diff|B layouts as a PDF for shareable reviews and archiving. Heatmap opacity is preserved.
Privacy First
All processing happens locally in your browser using PDF.js and companion libraries. No uploads—your files never leave your device.
How to Use the Tool
- Select PDFs: Load PDF A and PDF B (drag & drop or file picker).
- Pick Pages: Use page inputs or tap a thumbnail to jump to a page pair.
- Compare: Click Compare Current Page to render visuals and heatmap.
- Refine: Adjust threshold/opacity, toggle Ignore AA, Denoise, or Edge-Weighted to stabilize the diff.
- Zoom & Scroll: Use the zoom bar or Ctrl/Cmd+wheel; viewers stay synchronized.
- Text Diff: Run page-level or whole-document text comparison.
- Export: Download a two-up PDF (A|B, A|Diff, or A|Diff|B) for review.
Supported Operations
Visual Diff Modes
Heatmap: Blue → orange → red based on magnitude of change. Ideal for layout and graphic differences.
Binary: Clean red mask over changed pixels—great for strict pass/fail checks.
Pixelmatch: Classic image diff with adjustable threshold and anti-alias handling.
Enhancements
Denoise Blur: Smooths tiny speckles from rasterized text and scans.
Ignore AA: Suppresses anti-aliasing artifacts from rendering engines.
Edge-Weighted: Increases sensitivity along edges to spotlight shape and contour changes.
Technical Details
Built with modern web tech for fast, private comparisons:
- PDF.js: High-fidelity page rendering & text extraction
- Pixelmatch & custom shaders: Accurate pixel-level comparisons
- PDF-Lib: Client-side generation of two-up diff PDFs
- Mobile-First UI: Colorful tabs, accessible controls, smooth performance
Use Cases
Artwork & Layout QA
Catch misalignments, font substitutions, and color shifts between design revisions.
Contract & Policy Reviews
Verify every wording change using text diff while cross-checking layout changes visually.
Regulatory Filings
Compare versions of compliance documents and export two-up PDFs for audit trails.
Engineering & Specs
Highlight drawing and spec updates across iterations using edge-weighted visual diffs.
Privacy & Security
This tool operates with a strict privacy-first approach:
- No file uploads—processing is fully in-browser
- No tracking or external storage
- Temporary, memory-only rendering with automatic cleanup
Browser Compatibility
Works with modern browsers including Chrome, Edge, Firefox, and Safari. JavaScript required.