Type a word, set how strongly it shows, and it is stamped in bold across the middle of every page — at 35 degrees, or straight across if you turn the diagonal off. The size follows the page, so a long phrase comes out smaller to fit the same span. At the low end of the slider it is faint enough to read through; at the top it is impossible to miss.
The PDF engine (about 500 KB) loads only when you drop a file in, so the page itself stays light. Your file is read on your own machine and never sent anywhere. Open your browser’s network tab and watch while you use it.
Yes. Anyone with a PDF editor can. The text is drawn on top of the page as an ordinary object, which is what a watermark is: a visible label, not a lock. If you need a document that cannot be altered, no watermark provides that, and this one does not claim to.
Visually, yes — at the top of the slider the stamp sits in front of the words. What is underneath is still there, though, and this is the part worth being clear about: the text below a watermark stays selectable, searchable and extractable. We measured it on 2 September 2026 — a page stamped at the maximum 60 percent still gave up every word to the PDF-to-text tool on this same site, in one step. A watermark changes what a page looks like, not what it contains. If something must not be readable, it has to be taken out of the file before you share it; covering it over is not the same thing as removing it.
From the page, not from a fixed point size. The text is scaled to span the middle of the page, so a long phrase comes out smaller than a single word, and a small page gets a proportionally smaller stamp. There is no size setting to manage.
No. Every page gets the stamp. If only part of the file should be marked, split it first, stamp the part that needs it, and merge the halves back together. All three tools are on this site and none of them uploads the file.
These all work the same way, in your browser. Most are free; the ones marked as needing a plan are not.
A new DeskKit tool lands every week or two. Leave an address to hear about it. Nothing else is ever sent, and one click removes you.