A contract goes through three revisions before signing. A research paper gets resubmitted with minor edits. A code-of-conduct policy is updated annually. In every case, you need to know exactly what changed. Manual diff by reading both versions is slow and error-prone. PDFKits Compare PDF highlights differences between two PDF versions automatically — added text, removed text, repositioned content. Free, no signup, no upload.
The tool aligns the two documents by content (not just page number), so changes that shift content across pages are still detected. Differences are shown side-by-side with color coding: green for additions, red for deletions, yellow for moved/changed content. You can export the comparison as a third PDF with the differences embedded as annotations for review.
Drop the old and new versions of the document. PDFKits extracts text from both via pdf.js.
Click Compare. PDFKits aligns the two documents using sequence alignment algorithms, then highlights every difference at word and paragraph level. The side-by-side view shows the old version on the left and new on the right, with synchronized scrolling.
Step through differences with arrow keys or the difference list. Export the comparison as a third PDF where differences are embedded as visible annotations — useful for sharing the comparison with reviewers or saving for audit.
Legal teams compare contract versions during negotiation to spot every change the counterparty made — preventing surprise terms from slipping into the final version.
Auditors compare current vs prior-year policy documents to identify regulatory or operational changes that need disclosure or training updates.
Reviewers compare resubmitted papers to the originals to verify the requested revisions were actually made — and to spot unrelated changes that weren't part of the response to reviewers.
Teams without formal version control on PDFs use Compare to verify which version is the latest and what changed between versions stored in different folders.
Adobe Acrobat Pro DC includes Compare ($19.99/month). Online compare tools typically upload both files. PDFKits Compare PDF runs in your browser — both documents stay on your device throughout. Free, no signup, supports side-by-side view, difference list, and exportable comparison PDF.
Run OCR PDF first on both versions to add text layers, then compare. Comparison quality depends on OCR accuracy — for clean scans this works well.
Word-level additions and deletions, paragraph-level moves, formatting changes (font, size, color when these reflect meaningful changes), and image swaps. Whitespace-only changes are filtered out by default.
Yes — PDFKits aligns by content, not page number. Documents where chapters were reordered still compare correctly.
Yes for text within table cells. Visual table structure changes (merged cells, column reordering) are detected as paragraph-level changes.
Yes — if an image was replaced or repositioned, it's flagged. Pixel-level image diff is not currently supported (whether the same image was re-encoded differently isn't detected).
Practical limit is 100-200 pages per document for reasonable performance. Longer documents can be split first via Split PDF and compared piece by piece.