Add a text watermark to a PDF

What a watermark is actually for

A watermark communicates the status of a document to whoever is holding it. Its job is to prevent an honest mistake, not to stop a determined one. The mistakes it prevents are real and expensive: a draft contract circulated as though final, an old price list quoted a year later, a sample invoice pasted into a real accounting system, an internal memo forwarded outside.

The most valuable words on a watermark are usually the boring ones. DRAFT and NOT FINAL stop people acting on an unfinished document. A date — VALID UNTIL 31 DEC 2026 — stops a superseded version circulating indefinitely, and is far more useful than CONFIDENTIAL, which everyone has learned to ignore. For material shared with a specific party, their name across the page is the single most effective deterrent against onward sharing, because it makes the source of any leak obvious.

Making it readable without ruining the page

The whole design problem is that a watermark must be seen but must not interfere. Four settings control that balance, and they interact.

Opacity does most of the work. Somewhere between 12 and 25 per cent gives a stamp that is unmistakable at a glance and effectively invisible while reading. Above 30 per cent it starts to compete with body text; below 10 it may vanish entirely when printed on a laser printer, which handles pale greys poorly.

Angle matters more than people expect. Diagonal text crosses lines of body copy at an angle, so any given line of your document is obscured only briefly. Horizontal watermark text runs parallel to your paragraphs and can sit directly on top of a line for its whole length, which is much harder to read through. Forty-five degrees is the convention for good reason.

Colour should be light and low-saturation. Grey is the safest choice and prints predictably everywhere. Red reads as urgent and suits DRAFT. Avoid dark, saturated colours entirely — at any opacity that makes them visible, they fight the text.

Position is a choice between assertive and discreet. A single centred stamp is the standard. Tiled repeats the text in a grid, which is much harder to crop out and is appropriate for genuinely sensitive circulation. A line along the top or bottom is the discreet option, good for a version number or a date on a document that will be read closely.

The limits, stated plainly

A watermark is drawn content sitting on the page. Anyone with a full PDF editor can select and delete it in about thirty seconds, and rasterising or re-typesetting the document removes it just as easily. It is a label, not a lock.

So use it for what it is good at — making status unambiguous — and do not use it as a substitute for controlling who receives a file. If content must not be seen by particular people, the answer is not to send it to them, or to remove the pages containing it. A watermark solves an accident problem, and it solves it very well.