About highlight PDF differences
A list of differences is hard to circulate; a marked-up page is not. This tool runs the same pixel comparison and then renders the outcome as a new PDF in which changed regions are overlaid on the revised page, so a reviewer can see at a glance where to look. Differing pixels are grouped into contiguous regions and each region is boxed rather than shaded pixel by pixel, because a box around an altered paragraph communicates instantly while a speckled mask does not. Pages that are identical are marked as such rather than omitted, keeping page numbering aligned with the source documents. The output is an ordinary PDF, so it can be emailed, printed for a meeting or attached to a change request without the recipient needing this site or any tool at all. The reflow caveat carries over in full: if an early insertion shifted everything, most pages will be boxed and the markup will be true but unhelpful.
How to highlight PDF differences
- 01
Add both versions
Original first, revision second. Markup is drawn onto the revised pages.
- 02
Generate the comparison
Pages are rendered and compared locally, then differing regions are boxed.
- 03
Review before sending
Check whether markup is localised or everywhere — the latter means reflow, not substantive change.
- 04
Circulate the PDF
Send or print it. Recipients need nothing but a PDF reader.
What this tool does
- Output is a normal PDF anyone can open, print or attach
- Differing pixels grouped into boxed regions rather than a speckled pixel mask
- Unchanged pages retained and labelled so page numbers still line up
- Markup drawn on the revised version, so the reader sees the current text
- Comparison and PDF generation both happen in your browser
Limitations worth knowing
Every PDF tool has constraints. Stating them plainly is more useful than discovering them halfway through your work.
- Inherits the reflow problem: after an early insertion, nearly every page will be marked.
- Markup shows where something changed, not what changed or why.
- Slower than the report-only comparison because a new PDF has to be rendered and written.
- Documents with differing page counts cannot be aligned reliably, since pages are matched by number.
How your file is handled
This tool runs entirely inside this browser tab. When you choose a file, your browser reads it from your own disk and hands the bytes to JavaScript running on this page — no network request carries your document anywhere. You can confirm that yourself: open your browser’s developer tools, switch to the Network panel, and run the tool. You will see no upload.
Nothing is stored after the fact. Closing or reloading this tab discards the file, the result and everything derived from them, because none of it ever left your machine. Read how local processing works.
Questions about highlight PDF differences
Is the markup part of the original file?
No. A new PDF is produced and your source documents are untouched. The boxes exist only in that generated output.
Why are whole pages boxed instead of single words?
Usually reflow — everything below an insertion moved, so the changed region genuinely is most of the page. Run a text comparison to find the actual edit.
Can I send this to someone without technical tools?
Yes, that is the point of it. The result is an ordinary PDF that opens in any reader, which is why this exists alongside the on-screen comparison report.
Does it mark text changes as well as image changes?
Yes, because it works from pixels — changed words alter pixels just as moved images do. What it cannot do is tell you which category a given change belongs to.
Tools that pair with this one
- Visual PDF ComparisonCompare what the page looks like, not just what it says.
- Compare PDF FilesTwo versions in, a clear list of differences out.
- Compare PDF TextOnly the words, so a reformatted document still reads as unchanged.
- PDF Text DiffDiff semantics applied to PDF text, at word granularity.
- Watermark PDFDraw a text watermark across your pages, exactly where you want it.
- PDF to JPGRender each page of a PDF as a JPG image, at the resolution you pick.