Compare PDFs
Put two versions side by side and highlight every pixel that moved, so you can see exactly what changed between drafts.
Compare PDFs shows exactly what changed between two versions. Both files are rendered page by page and compared pixel by pixel; anything that moved is tinted, unchanged content fades to grey, and a percentage tells you how much differs. Download the diff as a PDF. Runs in your browser, free.
What is a PDF comparison?
What is a PDF comparison?
A comparison puts two versions of a document against each other and marks what differs. This tool does a visual diff: each page of both files is drawn to the same width, and the two bitmaps are compared pixel by pixel. Where the pixels differ beyond a tolerance you set, the diff view paints the accent colour; where they match, the page fades to light grey so changes stand out. A percentage of differing pixels is shown for each page.
Visual diff versus text diff
A text diff extracts the words from both files and lists inserted and deleted sentences. It is precise for prose but blind to layout, images, stamps and scans. A visual diff sees everything that renders: a moved logo, a changed figure, a new signature, an edit in a scanned page with no text layer. The trade-off is sensitivity: a one-line insertion reflows the rest of the page and the whole column shows as changed.
Why compare two PDFs?
- Proof before you sign. A counterparty sends back the "same" contract. Compare it to the version you approved and every altered clause lights up, including changes in tables and footers a text diff would not catch.
- Works on scans and images. Nothing needs a text layer. Compare a scanned signed copy against the original, or two versions of a floor plan or chart.
- Catch silent production changes. Reprints, regenerated reports and re-exported designs can shift in ways nobody mentioned. Pixels do not lie.
- Keep a record. The downloadable diff PDF is a page-by-page picture of what changed, ready to attach to an email or a file note.
- Never uploaded. Both files are rendered and compared in your browser.
How to compare two PDFs, step by step
- Open Compare PDFs and drop both files Drop two PDFs, the old version first and the new one second. They appear as A and B.
- Step through the pages Use the arrows above the view. The badge shows what percentage of pixels differ on the current page.
- Switch views Which version to show lets you flip between A, B and Diff. In Diff, changed pixels are tinted and unchanged content is faded.
- Adjust the tolerance The Tolerance slider (0 to 90 per colour channel) sets how different a pixel must be to count. Raise it to ignore anti-aliasing noise, lower it to catch faint changes.
- Click Download the diff as PDF One image page per page of the longer file, with the changes tinted, saved as
A-vs-B-diff.pdf.
Frequently asked questions
Is this a text comparison?
No. It compares rendered pixels, not extracted words, so it sees images, layout, stamps and scans, but it cannot list which sentence changed. For word-level diffs, export both files with PDF to Text and compare the text files in a diff tool.
Why does the whole page show as changed?
Usually because content reflowed: an added line pushes everything below it down, and every shifted pixel counts. Different page sizes or rotation have the same effect. Check the A and B views; if the pages line up visually, raise the tolerance to suppress anti-aliasing noise.
What happens when the files have different page counts?
Pages past the end of the shorter file are compared against a blank sheet, so they show as entirely changed, and a notice tells you which file the page exists in. The diff PDF has one page per page of the longer file.
Does it work on scanned PDFs?
Yes. Because the comparison is visual, a scan needs no text layer. Two scans of the same paper will differ slightly in position and noise, so raise the tolerance and expect a small background percentage even where nothing changed.
Is the diff PDF editable?
No. It is a visual record: each page is an image with the changes tinted. Use it as evidence or a review aid, and keep both originals for editing.
Looking for the long version? The guides cover each of these jobs in depth.