# Compare PDF Files

> Two versions of a contract — or two revisions of a drawing — in one diff view. Pick a document type (Document, AEC / Blueprint, or Image-Scan); the viewer lays the files side-by-side or as an overlay with a draggable slider and highlights changed pixels in red. In AEC mode a relocated symbol reads as "moved" and an in-place dimension edit as "modified", not delete-plus-insert. A separate Text Diff modal shows word-level changes. Both files stay in the browser tab — nothing touches a server.


Live tool: https://lofttools.com/tools/pdf-tools/compare-pdf

Category: PDF & Documents


## What it does

- Document-type selector — Document (contracts, reports), AEC / Blueprint (drawings, schematics), or Image-Scan
- AEC / Blueprint mode — word-level text diff for dimensions and title blocks, masked pixel diff for geometry (lines, circles, symbols)
- In-place revisions read as one "modified" entry (Ø8 → Ø10, rev A → B), not a separate add + remove
- Relocated symbols detected as "moved" instead of delete-plus-insert
- Change-location tags — every change labelled with its sheet region and X/Y position
- Side-by-side and overlay diff modes with draggable slider
- Word-level text diff with line numbers in a modal (split or unified)
- Pixel-level layout diff highlights — covers reflow, spacing changes, and image shifts (anything that changes the rendered page)
- Page rail with per-page diff badge + A/B preview stack
- Right pane comparing metadata, bookmarks, form fields, and fonts side-by-side
- Per-document transparent ruler (independent left/right) with px / in / mm units
- Export the marked-up comparison as a PDF
- Drag-rect exclusion zones to ignore page numbers / timestamps / margins
- Scroll to zoom, jump-to-next-change with F7 / Shift-F7
- Multi-page PDFs handled in browser memory (no per-page upload)
- Both source files stay in the browser tab — no server upload

## How it works

1. **Pick a mode and drop two PDFs** — Choose a document type — Document, AEC / Blueprint, or Image-Scan — then drop or pick an Original and a Modified PDF. Comparison fires automatically once both files are loaded.
2. **Compare** — Pixel diff with smart morphology runs in your browser; differences in text, images, and layout are highlighted on every page.
3. **Navigate changes** — Use the page rail, F7 to jump to the next change, or open the line-numbered text diff modal.

## FAQ

### What types of differences are detected?

Text additions, deletions, and modifications are highlighted. Layout and image changes are also shown.

### Can it compare engineering drawings or blueprints?

Yes — pick AEC / Blueprint mode. It runs a word-level text pass (dimensions, callouts, title-block revisions) alongside a masked pixel pass for geometry, so a relocated detail reads as "moved" and an in-place dimension change (Ø8 → Ø10) reads as one "modified" entry rather than a delete plus an insert. Each change is tagged with its sheet region and X/Y position.

### Does this preserve bookmarks and form fields?

Yes. The output PDF inherits bookmarks and form fields from the chosen base document; the diff overlay is added as annotations.

### What PDF versions are supported?

PDF 1.0 through 2.0 are diffed page-for-page. Encrypted files need to be unlocked first.

## Tips

- **Press F7 to walk every diff (`F7`)** — F7 jumps to the next changed region in order. Shift+F7 jumps back. No scrolling, no missed pages.
- **Works on flat scans too** — Compare PDF spots pixel-level differences even on scanned PDFs where text extraction fails. Useful for engineering blueprints and contracts.
- **Exclusion zones for noise** — Drag a rectangle to mark a region as ignore — useful for headers, page numbers, and timestamps that change but do not matter.
- **Files never upload** — Both PDFs stay in your browser. Compare confidential contracts and design files on shared computers safely.

## Privacy — what we do not do

This tool runs entirely in the browser via WebAssembly. Your file never reaches a Loft Tools server. Specifically:

- **No upload.** The file bytes load into the browser tab's memory and process on your own CPU. Open DevTools → Network and observe zero outbound requests carrying file data while Compare PDF Files runs.
- **No AI training on your file.** Loft does not train models. We could not train on a file we cannot see.
- **No content scanning.** No virus, copyright, or content-moderation pass against your file. The bytes are not accessible to us.
- **No server-side log of file contents, filenames, or EXIF metadata.** Cloudflare edge captures URL and truncated IP for abuse defense (standard CDN behaviour). Cloudflare Web Analytics records anonymous page hits, no cookies, no PII. Nothing about your file content reaches any log.
- **No retention.** Close the tab and the file leaves browser memory. No backups exist on our side because no copy ever existed on our side.
- **No account.** No email, no signup, no auth, no telemetry tied to you.
- **Offline-capable after first visit** (PWA). Once you've loaded a tool, it caches; later sessions work without internet. For high-sensitivity files, run the tool once online to warm the cache, then disconnect before processing.

Compare with upload-based services: each transmits your file to a processing server. Even over HTTPS, each has logs, retention windows, and subpoena exposure. Loft has none of these because the server architecture does not include your file.

## More

- All tools: https://lofttools.com/tools
- Category: https://lofttools.com/tools/pdf-tools
- LLM index: https://lofttools.com/llms.txt