What kind of watermark can I add to a PDF?

A diagonal text watermark placed at 45 degrees across the centre of every page, with controls for the text, font size, colour, and opacity (10-60%). The watermark is applied to all pages of the document. All stamping runs in your browser using pdf-lib.

Can I control how visible the watermark is?

Yes. The opacity slider controls transparency from subtle (10%) to strong (60%). Adjust it to keep the underlying content readable.

What angle is the watermark displayed at?

The watermark is placed diagonally at 45 degrees across the centre of each page, the standard position for document watermarks.

Can I watermark every page or just some?

The watermark is applied to every page in the document. Per-page watermarking is not currently available.

PDF Watermark

PDF watermark is a PDF tool that stamps a diagonal text watermark across every page of a document. It accepts any custom text (such as CONFIDENTIAL or DRAFT), exposes opacity, font size, and color controls, and applies a 45-degree rotation. The tool runs in your browser.

Drop a PDF here or click to browse

Dedicated pages

Direct links for specific watermarking tasks.

Add Watermark to PDF

Add a diagonal text watermark to every page of a PDF in your browser. Control text, opacity, size, and colour. No account required.

Watermark PDF Online

Add a text watermark to a PDF online. Set watermark text, opacity, font size, and colour. Free, private, runs in your browser.

Stamp PDF Pages

Stamp a text watermark on every page of a PDF file in your browser. Choose watermark text, opacity, size, and colour. All processing runs in your browser.

How to add a watermark to a PDF

Drop your PDF onto the upload area or click to browse.
Enter your watermark text (e.g. "CONFIDENTIAL" or "DRAFT") in the text field.
Adjust the opacity, font size, and colour to match your needs.
Click "Add watermark" and download the stamped PDF. All processing is in-browser.

Common uses

Marking draft documents with a DRAFT watermark before sharing for review, use text diff to track changes between draft versions
Adding a CONFIDENTIAL or SAMPLE stamp to a review copy before distributing
Watermarking shared drafts with a recipient name or reference number. Merge PDFs first if the document spans multiple files

Technical specification

Algorithm or formula: For each page, pdf-lib computes the page center, then calls page.drawText() with the watermark string, configured opacity, color, and a 45-degree rotation transform.
Browser API or library: pdf-lib for PDF write; embedded Helvetica from the PDF standard 14 fonts. Color values from rgb() helper and degrees encoded via the degrees() helper.
Input limits: PDF up to 100 MB. Watermark text up to ~80 characters fits comfortably across A4 / Letter pages.
Output: New PDF (application/pdf) with the same content plus the diagonal text overlay on every page, downloaded via Blob URL.
Known limitations: Single fixed angle (45 degrees) and centered position only. Image watermarks and per-page customization are not supported. Underlying text remains selectable beneath the overlay.

Frequently asked questions

Is my PDF uploaded to a server?: No. Watermarking uses pdf-lib running entirely in your browser.
Can I control how visible the watermark is?: Yes. The opacity slider controls transparency from subtle (10%) to strong (60%). Adjust it to keep the underlying content readable.
What angle is the watermark displayed at?: The watermark is placed diagonally at 45 degrees across the centre of each page, the standard position for document watermarks.
Can I watermark every page or just some?: The watermark is applied to every page in the document. Per-page watermarking is not currently available.

Reviewed and tested May 26, 2026.