PDF Watermark

How PDF Watermark works

Add a diagonal text watermark to every page of a PDF. Set the text, size and opacity; pdf-lib stamps each page in your browser and downloads the result. Everything happens inside this page: the tool reads your input, runs the calculation or conversion locally, and hands the result back to you. Nothing is transmitted, because there is no backend to transmit it to.

That design choice is deliberate. Most free tool sites upload your files to a server, process them there, and quietly keep a copy. Toolcin cannot do that — the site is a set of static files. If your connection dropped the moment the page finished loading, every tool would still work.

Drawn on every page

The watermark text is drawn onto each page at a rotated angle, with opacity set between 5% and 60% — 15% by default. Because it is written into the page content with pdf-lib, it moves with the page when the document is printed, copied or converted.

The output is a new PDF of the same page count. The original is untouched, so the unwatermarked file still exists if you need it.

Choosing an opacity that works

At 0.15 the mark is visible on screen and faint when printed; at 0.05 it is nearly invisible on a laser printer. Anything above 0.3 starts to interfere with body text underneath.

Grey or a light tint reads better than pure black, because black at low opacity still darkens the text it crosses.

What a watermark is for

Marking a draft, a confidential document or a sample so that a leaked copy carries its origin. It does not prevent copying — the text is still selectable — but it does make an uncontrolled copy traceable to its source.

For real protection you need encryption or a signature, not a visual mark.

Good to know

• Works offline once loaded, including on flights and in locked-down networks.
• No file size limit beyond your device's own memory.
• Free to use, with no account and no usage counter.
• Results are produced locally, so they are not logged or shared with anyone.

Questions