Mark every page
A watermark tells anyone holding the document what it is: a draft not to be quoted, a copy for one recipient, confidential material. Type the text, choose how visible it should be and press Add watermark.
- Text: short words work best, such as
CONFIDENTIAL,DRAFT,COPYor a name and date. The size adjusts so it spans the page. - Opacity: 15 % is subtle, 25 % is clearly visible while the page stays readable, 40 % is bold.
The watermark runs corner to corner in red across every page, including rotated ones, and is added as text on top of the content. You can watermark up to five PDFs at once.
A watermark is a label, not a lock: someone with editing software can remove it. To stop people opening a file, use Protect PDF.
Private
Your PDF is stamped by your browser on your device; it isn't uploaded.
How this works
The PDF is opened in a Web Worker with pdf-lib. For each page the tool measures the visible diagonal, picks a font size that makes your text span most of it, and draws the text in bold Helvetica at the chosen transparency, centred and angled along the diagonal. Standard PDF fonts cover Western European characters, so accented words work; other characters are replaced with a question mark.
Frequently asked
Can the watermark be removed?
By someone with PDF editing software, yes. A watermark labels a document; to restrict who can open it, add a password with Protect PDF.
Can I use accented words?
Yes. Western European letters such as é, ç and ã work. Characters outside that set are replaced with a question mark.
Is my PDF uploaded?
No. The watermark is added by your browser on this device.
Will it cover the text underneath?
It sits on top but is semi-transparent; at 15 % or 25 % the page stays easy to read.
Sources
- ISO 32000-2:2020 — Document management — Portable document format — Part 2: PDF 2.0
- @cantoo/pdf-lib — create and modify PDF documents in any JavaScript environment
- Wikipedia — PDF
Reviewed Oct 19, 2026 · test vectors fixtures/tools/pdf/watermark-pdf/