A watermark is a piece of communication, not a security measure, and almost everything that goes wrong with them comes from confusing the two. Someone stamps CONFIDENTIAL across a document, sends it out, and believes something has been protected. Nothing has. The word is a note to the reader — a useful one, which is why the tool exists — but it is a label on a box rather than a lock on it.
So this page says that up front, and the tool repeats it where the decision is made. If what you need is a document that cannot be opened by the wrong person, that is a password. If what you need is a document whose every page says DRAFT so nobody quotes the wrong version back at you, this is exactly right.
The part that is usually badly done is the preview. Most tools show you a thumbnail, or a sample page, or nothing at all until the download. Here every control acts on your own first page as you touch it: type a word and it appears, drag the strength down and it fades, move it to a corner and it goes. Nine positions, three sizes, three strengths, and one choice that matters more than it looks — in front of the text or behind it.
Behind is usually the better-looking answer, because the words stay easy to read. It has one real cost, and the tool states it rather than letting you find out: a stamp behind the page content is invisible wherever the page is solid, so a full-width photograph or a filled table will hide it completely. That is worth knowing before you send twelve pages out with a stamp on nine of them.
Free, no signup, no cap on pages, and no watermark of ours on top of yours — which is not a joke so much as a thing other free tools genuinely do.