How to add a watermark to a PDF
- Drop a PDF onto the drop zone above, or click to choose it.
- Type your Watermark text. The default is
CONFIDENTIAL; common alternatives areDRAFT,COPY,SAMPLEor a company or recipient name. - Set the Opacity (5–80%; 20% by default) and the Font size (60 pt by default).
- Leave Diagonal ticked for the classic corner-to-corner stamp, or untick it for horizontal text.
- Click Add watermark and download the stamped PDF. The text is centred on every page in a translucent red, bold typeface.
The watermark is drawn with pdf-lib inside your browser, so the document you are marking as confidential is never uploaded to anyone.
What a text watermark does (and doesn't) do
A watermark is semi-transparent text drawn over the page content. It communicates the status of a document at a glance (draft, internal, void) and discourages casual re-use, because every printout and screenshot carries the mark.
It is important to understand that a watermark is a visual deterrent, not a security control. The text is added as an extra layer of page content. Determined users with PDF editing software may be able to remove or cover it, and it does not stop anyone from opening, copying or printing the file. For truly sensitive documents, combine watermarking with access controls on where the file is stored and shared.
Choosing the right settings
| Setting | Lower value | Higher value |
|---|---|---|
| Opacity | Subtle; the document stays easy to read (10–25%) | Bold; hard to ignore, but can obscure text (40%+) |
| Font size | A discreet label, good for long names | A large stamp that spans the page |
| Diagonal | Diagonal text crosses more of the content, so it is harder to crop out; horizontal text is neater and easier to read | |
As a starting point, keep the defaults for short words such as DRAFT. For longer text, such as Prepared for Acme Ltd, reduce the font size so the whole phrase fits on the page.
Tips
- Personalised copies: putting the recipient's name in the watermark makes it obvious where a leaked copy came from. Generate one version per recipient.
- Watermark as the last step. If you are combining files, join them first with Merge PDF so every page of the final document is stamped.
- Need page numbers as well? Add them with Add Page Numbers to PDF.
- Image-based compression flattens everything into a picture, which bakes the watermark into the page. If that is what you want, use the Recommended mode of Compress PDF; note that text then stops being selectable.
- The watermark uses the standard Helvetica Bold PDF font, which covers Western European (Latin) characters. Text in other scripts, such as Cyrillic, Greek, Arabic or Chinese, cannot be used. Text is limited to 80 characters.
- Password-protected or encrypted PDFs are not supported. Unlock it first with Unlock PDF (you need its password), then come back.
Frequently asked questions
Is the watermark added to every page?
Yes. The same text, size, opacity and angle are applied to all pages of the document.
Can people still read and select the original text?
Yes. The watermark sits on top of the content as a translucent layer, so the underlying text remains readable and selectable, especially at lower opacity.
Can a watermark be removed?
Someone with PDF editing software may be able to remove it, so treat a watermark as a deterrent rather than protection. Keep your unwatermarked original in a safe place.
Can I change the colour or use a logo?
No. This tool adds text watermarks in a fixed red colour, with adjustable text, size, opacity and angle. Company names, labels and recipient names work well as text.