Overview
Compares two versions of a PDF and shows what text changed. It extracts the text of both files, compares page n of the original with page n of the new version line by line, and highlights added and removed lines. Changed pages are flagged, any page can be shown side by side, and the full diff downloads as a text report. Both files are read in your browser.
How It Works
Drop the original PDF on the left and the changed version on the right, then click Compare PDFs. A summary says how many pages differ and whether the page counts match. Each page lists its added and removed line counts; expand Side by side to see both pages rendered next to each other. Options ignore spacing differences and upper or lower case, and switching them updates the result instantly. Diff report saves every change as a .txt file.
Step-by-Step Usage Guide
- Drop the original PDF on the left and the revised one on the right.
- Choose whether to ignore spacing and letter case.
- Click Compare PDFs.
- Review flagged pages and open Side by side where needed.
- Download the diff report if you need a record.
Technical Specifications & Standards
Text is extracted from each page with pdf.js and grouped into visual lines by baseline, so a sentence split into several runs still compares as one line. Pages are paired by number, and each pair is compared with a longest common subsequence diff, the same idea used by version control tools: shared lines at the start and end are matched first, and the middle is aligned so the smallest set of added and removed lines is reported. Ignoring spacing collapses runs of spaces, which hides differences caused by justification or kerning. When one file has more pages, the extra pages are listed as only in A or only in B. Because pages are compared by position, inserting a page early in the document makes every later page look changed; check the page counts first. Formatting, colours and images are not compared, and scanned PDFs need OCR before they have text to compare.
Targeted Use Cases
- Checking what a counterparty changed in a returned contract.
- Reviewing edits between two drafts of a policy or report.
- Confirming that only the agreed corrections were made in a reprint.
- Spotting price or quantity changes between two versions of a quote.
Notes & Gotchas
- Compare files exported the same way, since different PDF tools break lines differently.
- Keep Ignore spacing on unless whitespace itself matters.
- Check page counts first, because an inserted page shifts every later comparison.
Frequently Asked Questions
How do I compare two PDF files for differences?
Drop the original and the revised PDF, then click Compare PDFs. Added lines are highlighted in green and removed lines in red, page by page.
Does it compare images and formatting?
No. Only text is compared. Use Side by side on a flagged page to check layout, images and formatting visually.
Why does every page after page 3 show changes?
Pages are compared by position, so a page inserted or removed early shifts the rest. Remove or add that page in one file first, then compare again.
Can I compare scanned PDFs?
Not by text, because scans have no text layer. Run OCR on both files first, or use Side by side to compare the page images by eye.
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