A watermark says something about the status of a document to anyone who looks at it. DRAFT so nobody acts on a version that is still changing. CONFIDENTIAL so a printed copy left on a desk carries its own warning. SPECIMEN, VOID, COPY, or a client name on work that has not been paid for yet.
How it is drawn
Your text is placed diagonally across the centre of every page at 30 degrees, in grey at 25% opacity, sized to span the page. It sits above the existing content so it is always visible, but the transparency keeps the document readable underneath — which is the point, since an unreadable watermarked document is no use to the person reviewing it.
The size adapts to the length of the text. A short word like DRAFT is drawn large; a longer phrase such as "CONFIDENTIAL — DO NOT DISTRIBUTE" is drawn smaller so it still fits. Keep it short for the strongest effect.
This is not security
Being direct about this, because watermarking is often mistaken for protection. The watermark is a layer of text drawn on top of the page. Anyone with a PDF editor can remove it in about thirty seconds. It does not encrypt the document, prevent copying, stop printing, or track where the file goes.
What it does is communicate. It stops an honest person circulating a draft by accident, and it makes a printed page carry its own context. Those are real and useful things. They are not the same as stopping a determined person from doing anything.
- For genuine access control, use password encryption in a PDF reader — and note that this site cannot open encrypted files afterwards.
- For proof of origin, a digital signature is the tool, not a watermark.
- For anything truly sensitive, do not send the file at all.
- For preventing edits, nothing in the PDF format is reliable; the format was designed for fidelity, not restriction.
What happens to the document
Page content is copied rather than re-rendered, so text stays selectable, images keep their original bytes and the file grows by only a few kilobytes. The watermark is real text rather than an image, so it prints crisply and scales at any zoom.
Apply it last, after any merging or reordering, and keep your unwatermarked original — removing the mark later is not something this site can do. Everything runs in this tab, so a confidential document does not have to be uploaded to be labelled confidential.