PDF Watermark Stamper
Add a text or image watermark like CONFIDENTIAL to every PDF page in your browser, with no upload.
- Runs in your browser, files never leave your device
- Free, open source, no account, no ads
- Works offline after the first visit
Add a watermark to a PDF
Drop a PDF here or choose a PDF
Nothing is uploaded. Everything happens on this device.
Your document stays on this device. The PDF is opened and stamped by your browser, so contracts, reports and drafts are never sent to a server. Pick a PDF, choose a text like CONFIDENTIAL or a PNG or JPG logo, check the preview and download the stamped copy.
The standard PDF fonts only cover Latin letters, so some of these characters cannot be stamped as text. Turn the text into an image instead: it keeps every character and works the same way.
How it works
- Open your PDF. Drop it on the page or choose it. Your browser reads it locally; nothing is uploaded.
- Set up the stamp. Type a text like CONFIDENTIAL or DRAFT, or pick a PNG or JPG logo. Choose opacity, angle, center or tiled, the layer and which pages to mark, and check the live preview.
- Apply and download. The stamp is drawn into the PDF on your device and saved as name_watermarked.pdf. The rest of the page content is left as it was.
Questions, answered
Are my files uploaded anywhere?
No. PDF Watermark Stamper runs entirely in your browser. Your PDF and your logo are read into memory on your device, stamped with JavaScript, and never sent to a server. You can disconnect from the internet and it keeps working.
Is it really free?
Yes. It is open source under the MIT license, with no account, no daily limits, no paid tier for image stamps and no ads. If it saves you a paid subscription, you can say thanks on Ko-fi.
Can I stamp text in Hebrew, Arabic, Chinese or with emoji?
The built-in PDF fonts (Helvetica, Times, Courier) only cover Latin letters. When your text has other characters, the tool offers a button that draws the text into a transparent image with your system fonts and stamps that image instead, so every character shows up.
What is the difference between over and under the content?
Over puts the stamp on top of everything, so it is always visible. Under paints it first and lets the page draw over it, which keeps text easy to read. If a page has a solid white background (common in scanned PDFs), an under stamp is hidden by it, so use over for scans.
Does it work offline?
Yes. After your first visit the page is cached by a service worker, so it loads without a connection. You can also install it from your browser's menu as an app.
Was this written by AI?
Yes. PDF Watermark Stamper was generated by Claude Code from a written specification inside an automated pipeline, with a test suite that runs in a real browser. The full source is on GitHub, so you can read every line before you trust it with your files.
Built by one person, given away for free
PDF Watermark Stamper is a free alternative to paid tools like Smallpdf and iLovePDF Watermark PDF. If it earns a place in your bookmarks, a coffee keeps the updates coming.
☕ Support Or on Ko-fi