Guide · 2 min read
How to Compare PDF Files
Find differences between two PDFs with side-by-side view or visual pixel diff.
Maintained by Leslie · Updated
Examples describe expected workflows unless a dated test is explicitly identified. Check the downloaded result against your own document before sharing it.
Why compare PDFs
Compare PDF helps you spot changes between document versions. Upload the original and revised PDFs to see what was added, removed, or modified.
Two modes are available: Side by side shows both documents next to each other, and Visual diff highlights changed pixels in red.
Comparison steps
Upload the original PDF first, then the revised version. Choose Side by side for a page-by-page view or Visual diff for change highlighting.
Click Compare PDF and download the comparison document to review or share.
What comparison detects
The tool detects visual changes on each page. Text edits, formatting shifts, and image changes are highlighted in the visual diff mode.
Scanned PDFs can be compared directly; OCR is not required. Pages are paired by page number, and extra pages in the longer file are omitted. Visual diff scales the revised page to the original page dimensions and highlights pixel differences, not semantic text edits.
Check pagination before trusting highlighted differences
An original with five pages and a revision with six produces only five paired comparison pages here. The sixth revision page is omitted. Check counts in both originals before comparing and review any unmatched pages separately.
If a new page was inserted at position 2, original page 2 is compared with the inserted page, not its corresponding revised content. Many red marks may therefore mean misaligned pages rather than widespread edits. Align matching sections first or compare the originals manually.
Use visual differences as review leads
For a price-list revision with unchanged pagination, inspect changed prices and their surrounding headings in both sources. A small numerical edit can matter more than a large highlighted logo. Pixel differences show where rendered images differ; they do not explain which text was added or whether a change is correct.
Scans with different skew, exposure, or resolution can produce broad highlighting. The visual-diff mode scales the revised page to the original dimensions, so also check actual page sizes. The output is an image-based comparison PDF, not a complete textual change log.