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

  1. Select PDFs: Load PDF A and PDF B (drag & drop or file picker).
  2. Pick Pages: Use page inputs or tap a thumbnail to jump to a page pair.
  3. Compare: Click Compare Current Page to render visuals and heatmap.
  4. Refine: Adjust threshold/opacity, toggle Ignore AA, Denoise, or Edge-Weighted to stabilize the diff.
  5. Zoom & Scroll: Use the zoom bar or Ctrl/Cmd+wheel; viewers stay synchronized.
  6. Text Diff: Run page-level or whole-document text comparison.
  7. 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.