Add Watermark to PDF

Stamp a diagonal text watermark on any PDF — free and private.

Custom watermark text — any word or phrase
Adjustable opacity (10%–80%)
Diagonal placement across every page
No cloud processing — runs in your browser

NilPDF Watermark stamps your chosen text diagonally across every page of your PDF — entirely in your browser. Adjust the font size and opacity to suit your needs, then download the watermarked file instantly. Common uses include marking drafts as CONFIDENTIAL, DRAFT, or DO NOT COPY before sharing.

100% private. Your files are processed entirely inside your browser using WebAssembly. Nothing is uploaded to any server. NilPDF has no backend — there is no server to send your files to.

Frequently Asked Questions

Is adding a watermark to a PDF really free?

Yes — completely free, unlimited use, no account required.

Are my PDF files safe when I watermark them?

Your files never leave your device. All processing happens in your browser using WebAssembly (Pyodide). NilPDF has no server — there is nothing to upload to.

Can I control how big the watermark is?

Yes — you can adjust the font size and opacity from the tool settings.