PDFStack Tool
Add Watermark to PDF — Free Online Tool
Stamp a custom text watermark — CONFIDENTIAL, DRAFT, DO NOT COPY, or any text you choose — across every page of a PDF. Control the font size, transparency, and rotation angle to get exactly the look you need.
Open Watermark PDF →
No file uploads
No account required
Free to use
Private & secure
Why watermark PDFs?
Watermarks deter unauthorised reproduction, signal document status (Draft, Approved, Confidential), or identify the intended recipient of a document. PDFStack bakes the watermark directly into the PDF's page content using pdf-lib, making it part of the document rather than a removable layer.
How to add a watermark to a PDF
- 1Open Watermark in PDFStack.
- 2Upload your PDF.
- 3Enter your watermark text, set font size, opacity (0–1), and rotation angle.
- 4Click Add Watermark and download the watermarked PDF.
All processing happens locally in your browser — no files are uploaded to any server.
Common Uses
Marking draft documents, watermarking confidential reports, adding 'SAMPLE' to PDF templates, protecting distributed copies with recipient names.
Frequently Asked Questions
Can I control the watermark position?
The watermark is centred diagonally by default. Adjust the rotation angle to change orientation.
What opacity should I use?
0.10–0.20 is typical for a subtle background watermark. Increase for a more prominent stamp.
Can the watermark be removed?
PDFStack embeds the watermark in the page's content stream, making it much harder to remove than a layer-based watermark.
Is my PDF private?
Yes. Watermarking runs entirely in your browser.