Watermark PDF
Stamp a diagonal text watermark across every page of a PDF, on your device.
Watermarked PDF ready.
How it works
This tool opens your PDF in the browser with the pdf-lib library and draws your chosen text diagonally across the centre of every page, rotated at 45°, then saves a brand-new copy. It adds the watermark as a semi-transparent text layer rather than re-rendering the pages, so the original content stays crisp and selectable underneath. Everything happens locally on your device — the document, often a draft or a confidential file, is never uploaded to any server.
How to watermark a PDF
Drop your PDF into the box, or click to browse for one. Type the label you want — it defaults to CONFIDENTIAL, but you can write anything such as Draft, Sample or your company name. Pick a size (Small, Medium or Large), an opacity (10% to 50%) and a colour (grey, red or blue), then click Add watermark. A progress bar ticks through the pages (for example Page 3 / 12), and once it finishes you download the result as a .pdf file.
A concrete example
Imagine you have a twelve-page contract you're about to share with a prospective client. You drop it in, set the text to CONFIDENTIAL, choose a Medium size with 20% opacity in grey so the contract stays readable, and click Add watermark. In a few seconds all twelve pages come back stamped, the watermark running diagonally across the centre of each one. You download watermarked.pdf and send that version, while your untouched original stays exactly where it was on your computer.
What to expect
The watermark is applied to every page in a single pass, using a bold Helvetica typeface that spans the middle of the sheet diagonally. Three sizes control how large it appears, four opacities balance visibility against readability, and three colours cover neutral, warning and brand use cases. Your original file is never modified — the tool works on an in-memory copy and hands you a separate download, so you can re-run it with different settings without risk. The output is a standard PDF you can view, print or share like any other.
Common problems and fixes
You forgot to type any text — the tool asks you to enter a watermark text first, so add a label before running. The watermark hides too much of the document — lower the opacity to 10% or 20% so the content beneath stays easy to read. It looks too faint to matter — raise the opacity to 35% or 50%, or bump the size up to Large. The file won't open in the tool — make sure you're dropping a real PDF (application/pdf); other formats are rejected by the file picker. You changed your mind — just pick a new size, colour or opacity and run again; your original stays untouched throughout.
Frequently asked questions
Can the watermark be removed?
It's drawn into the page content, so a normal reader can't toggle it off. Dedicated editing tools could still remove it, so it deters rather than permanently locks.
Does it cover every page?
Yes, the same watermark is applied to all pages of the document in a single pass, automatically.
Will the underlying text still be selectable?
Yes. The watermark is an added layer, so the original text and images remain intact and selectable beneath it.
Is my PDF uploaded to a server?
No. The whole process runs in your browser with the pdf-lib library; nothing leaves your device.
Can I change the font or the angle?
Not in this tool. The text uses a bold Helvetica and is always tilted at 45°, but you can adjust its size, opacity and colour.
Does it work on multiple pages of a large document?
Yes. Larger files simply take a little longer — the progress bar shows the current page, so you can follow it through to the end.