Overlay two PDFs to compare them
Import two versions of the same document (for example before and after proofreading): each page of the second document is overlaid with transparency on the matching page of the first, so you can spot layout or content differences at a glance.
How it works
Each page of document A serves as an opaque background; the page with the same number from document B is redrawn on top with the opacity you choose, centered and scaled if the two documents don't have exactly the same page size. Areas where the text or graphics differ then show up as a double image or visual blur.
What happens if the two PDFs don't have the same number of pages?
The tool generates as many pages as the longer of the two documents. A page that exists in only one of the two files is shown alone, with a note at the top of the page saying it's missing from the other document.
Does this tool detect differences automatically?
No, it doesn't compute a text diff: it produces a visual overlay that lets you spot differences by eye. For an automatic text comparison, use the site's dedicated PDF text comparison tool instead.
The overlay is composed entirely in your browser with the pdf-lib library — your two documents are never sent to a server.