Add a Watermark to a PDF
Stamp a diagonal text watermark across every page, like CONFIDENTIAL or DRAFT. Pick the text, size, color, opacity, and angle. Nothing is uploaded, it all happens on your device.
Click to choose a PDF file, or drag and drop it here
Stays on your device, nothing is uploaded.
A rough approximation on a standard page, the real result depends on your PDF's actual page size.
Are my PDF files uploaded anywhere?
No. The watermark is added entirely inside your browser using JavaScript. Your files never leave your device or touch a server.
Can I change the watermark's angle and transparency?
Yes. Set the rotation angle in degrees and the opacity as a percentage, 0% is invisible, 100% is fully solid.
Does the watermark go on every page?
Yes, the same watermark is stamped on every page of the document.
Can I remove a watermark this tool added?
Not with this tool, the watermark becomes part of the page content. Keep a copy of your original file if you might need it without the watermark later.
Can I watermark a password-protected PDF?
Not currently. Password-protected or encrypted PDFs can't be read by the tool and will show an error, remove the password first with a PDF reader.
How it works
Your PDF is loaded by pdf-lib, which edits the file's object structure directly in
browser memory. For each page it measures the watermark string in Helvetica Bold at your
chosen size, finds the page's exact center from its own dimensions (so mixed portrait
and landscape pages each get a properly centered stamp), and appends one text-drawing
instruction to that page's content stream. The opacity is real PDF transparency, an
ExtGState alpha value, not a washed-out gray color, so the watermark blends
correctly over photos and dark backgrounds, not just white paper. Rotation follows PDF
convention: positive angles turn counterclockwise, which is why the classic diagonal
"DRAFT" is +30 or +45 degrees.
Because it's drawn as real vector text, the watermark stays razor sharp at any zoom level and adds only a few hundred bytes per document, no page is rasterized and nothing already in the file is recompressed. The live preview approximates the same math in CSS so what you see before clicking is what pdf-lib draws.
Be honest with yourself about what a watermark is, though: it's a deterrent, not a lock. The text is stamped on top of the page content as an ordinary drawing operation, and anyone with a full PDF editor can select and delete that object. That's true of virtually every watermark tool, including the paid ones. It reliably marks a document as a draft or as confidential; it does not make copying impossible.
Since watermarked files are often exactly the sensitive kind, verify the privacy claim: open the DevTools Network tab and apply a watermark. Nothing is transmitted. The file is modified in memory and downloaded from a local blob without leaving the tab.