PDF Difference Highlighter
Visually compare two PDFs pixel by pixel and highlight differences in red, page by page. Free, private, runs entirely in your browser.
First PDF
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Your file never leaves your browserSecond PDF
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Your file never leaves your browserHow This Tool Differs From "Compare Two PDFs"
This site's Compare Two PDFs tool compares the extracted text of two documents word-by-word. This tool works differently: it renders each page of both PDFs to an image and compares them pixel by pixel, which catches visual changes that text comparison can't — moved images, shifted layout, changed colors, or edits inside a scanned/image-only PDF with no text layer at all.
How to Use It
- Upload the original PDF and the modified version.
- Click Highlight Differences — each corresponding page pair is rendered and compared pixel by pixel.
- Any pixel that differs beyond a small tolerance (to ignore anti-aliasing noise) is highlighted in red on the output image; matching areas are shown dimmed for contrast.
- Review each page's diff percentage and image, or download a single PDF report containing every diff image.
Example
Two versions of a scanned invoice where only the total amount changed will show a small red patch right over that number, with the rest of the page shown dimmed and unchanged — even though neither PDF has a text layer for a text-based comparison to use.
Common Use Cases
- Verifying that a re-exported or re-scanned document didn't shift or change visually.
- Spotting layout or image changes between two design proofs that text comparison would miss.
- Comparing scanned or image-only PDFs that have no extractable text at all.
FAQ
- What happens if the two PDFs have different page counts? Only pages up to the shorter document's page count are compared; a warning notes the mismatch and how many pages were skipped.
- Why do minor formatting differences show up as red everywhere? If the two PDFs are laid out slightly differently (different page size, shifted margins), corresponding pixels won't line up and will register as differences across large areas. This tool assumes both pages are meant to look the same overall.
- Does this replace the text-based Compare Two PDFs tool? No — they answer different questions. Use text comparison for wording changes, and this tool for visual/layout changes.
- Is my file uploaded anywhere? No — both files are processed and compared entirely in your browser.