What is PDF comparison?
PDF comparison analyzes two versions of a document side-by-side and highlights every textual, visual, and structural difference between them. It is widely used in legal redlining, contract negotiation, and quality assurance to catch edits, deletions, and formatting changes that the human eye would miss.
Compare PDF Files Online Free
Compare two PDFs side-by-side with visual diff view. Spot every text, image, and formatting difference. AI-powered, exportable reports. Free, no signup.
Key Features
- Side-by-side and overlay views — synchronized scroll keeps the same page visible in both versions
- Line-level text diff — LCS algorithm with intra-line word highlighting (red strikethrough for removed, green underline for added)
- Pixel-level visual diff — shows layout shifts, image changes, color differences with adjustable threshold
- AI semantic mode (opt-in) — detects reworded paragraphs that text-diff misses, labels them "reworded" instead of separate add+remove
- Page-level summary — total pages added / removed / changed, percentage change per page
- Ignore whitespace + ignore case toggles — hide cosmetic-only differences for clean redline review
- Per-page heatmap — quickly find pages with the most changes
- Export diff report as PDF — sharable summary with thumbnails and change counts
- Browser-side — neither original nor revised PDF leaves your device
About PDF Compare
PDF Compare shows you exactly what changed between two versions of a PDF — text differences, layout shifts, added or removed pages, and now reworded clauses caught by AI semantic comparison. Side-by-side preview with synchronized scrolling, color-coded line-level diff (green = added, red = removed, amber = modified), and pixel-level overlay for visual layout drift.
Standard PDF diff tools only catch text-identical changes. If a clause is rephrased — same meaning, different words — they show it as separate add + remove rows. Ours runs an opt-in AI semantic pass (browser-side MiniLM) that detects semantic matches between added and removed text and labels them as "reworded" instead, so contract redline review is actually readable. No upload, no signup, runs in your browser via pdfjs + pdf-lib.
Who Uses This Tool
- Lawyers redlining contracts — see exactly what the other side changed in the latest revision, including reworded clauses
- Compliance teams comparing policy documents across versions — highlight every textual change for audit trail
- Engineers diffing technical specifications — catch silent changes to requirements or scope
- Editors comparing manuscript drafts — see what an editor changed before accepting / rejecting edits
- Real estate transactions — diff offer letters, disclosures, addenda across negotiation rounds
- Government bid responses — track changes between draft and final RFP responses
How to Use Compare PDF Files Online Free
- Step 1: Upload original PDF (left side) and revised PDF (right side) — both render in parallel
- Step 2: Heatmap shows per-page change density — click any page to dive into line-level diff
- Step 3: Toggle "Ignore whitespace" and "Ignore case" to hide cosmetic-only differences
- Step 4: Click "AI Compare" to run the semantic pass — reworded paragraphs are merged into single "reworded" rows instead of separate add+remove
- Step 5: Export the diff report as PDF for your records, or screenshot the side-by-side view for stakeholder review
Frequently Asked Questions
Is PDF Compare free?
Yes — text diff, pixel diff, and AI semantic mode are all free with no signup. No file size limits beyond browser memory. Side-by-side preview, heatmap, and export are all included.
Does it work on scanned PDFs?
Pixel-level visual diff works on any PDF including scans. Text-level diff requires extractable text — for scanned PDFs, run OCR first (our OCR PDF tool), then compare the OCR'd versions.
What is the AI semantic mode?
Standard diff says "this clause was removed AND this other clause was added." AI semantic mode notices the two are 80% similar in meaning and labels them as "reworded" instead — one row, not two. Especially valuable for contract redlines where clauses are renumbered or rephrased rather than truly changed.
Can I compare two versions of a contract?
Yes — that's the most common use. Use AI semantic mode for the cleanest output. Export the diff report as PDF to share with the other side for redline negotiation.
Are my files secure?
Yes — both PDFs render and diff entirely in your browser via pdfjs-dist. Neither file is uploaded. The AI semantic pass uses an on-device 5 MB model (MiniLM) — that also runs in your browser.
Can I compare PDFs of different page counts?
Yes — pages-only-in-A and pages-only-in-B are flagged in the heatmap. Aligned pages show line-level diff; orphan pages are previewed alongside.