Stamp a PDF with text or a logo without ruining readability

A watermark does two jobs. It tells anyone looking at a page what the document's status is, and it makes casual reuse awkward. It is worth being clear that neither of those is protection, because a lot of watermarking is done in the belief that it is.

Get the visual settings right

Most bad watermarks fail on one of four settings, and the watermark tool exposes all of them.

Opacity. This is the one that matters most. Somewhere between 10 and 25 percent is the useful band: unmistakable when you look for it, invisible enough that you can still read the paragraph underneath. Above 40 percent the document becomes tiring to read; below 8 percent the mark disappears when printed on a tired office printer.

Angle. A diagonal mark of about 45 degrees is conventional for a reason. It crosses more of the page than a horizontal mark, it is harder to crop out, and it reads as a deliberate stamp rather than as part of the content.

Size and position. One large diagonal mark across the centre is the standard for status labels like DRAFT or CONFIDENTIAL. Tiled repetition — the same mark repeated in a grid — is harder to remove by cropping and is worth using for material you expect to be circulated. A small corner mark is right for a logo you want present but not intrusive.

Colour. Mid grey is the safest choice. It shows on white, prints predictably, and does not compete with coloured content. Saturated red on a page of charts turns into noise.

Text or image

Text watermarks suit status and ownership labels: DRAFT, CONFIDENTIAL, NOT FOR DISTRIBUTION, a recipient name, a date, a case reference. They are crisp at any zoom, tiny in file size, and legible when printed.

Image watermarks suit brand marks and seals. Two things to check: use an image with a transparent background, or you will stamp a white box across the page; and start from a high-resolution source, because a small logo scaled up across a page looks visibly rough.

A recipient-specific text watermark deserves a special mention. Stamping each copy with the name of the person it went to does not stop a leak, but it does make an unattributed leak much less likely, because the leaker knows the copy is identifiable. That is the strongest deterrent effect watermarking actually has.

Be honest about what it protects

A watermark is applied to page content. Anyone holding the file can:

• crop the page to remove a corner mark
• cover it, or edit the content stream in a capable editor
• select and copy the underlying text, which the watermark does not touch
• print, photograph, or re-scan the page

So watermarking is a social control, not a technical one. It communicates intent and raises effort. If the requirement is that unauthorised people cannot read the document, that is a job for encryption — and if the requirement is that specific content must not be visible at all, that is a job for redaction.

Watermarking pairs well with both. A confidential document can reasonably be redacted, watermarked with the recipient's name, and then encrypted for delivery.

Flatten when you are finished

Depending on how it is applied, a watermark can exist as an annotation layered over the page rather than as part of the page itself. Annotations can be selected and deleted in an editor, and some readers do not print them at all — which produces the worst outcome, a document that looks marked on screen and prints clean.

Running the result through the flattening tool merges the mark into the page content. After that it prints everywhere, displays identically in every reader, and cannot be removed by clicking on it.

Keep an unmarked original. Flattening is deliberately one-way, and the version you archive should not be the one stamped DRAFT.

When a header or footer is the better answer

If what you actually need is a document reference, a date, a classification line, or a filename on every page, a watermark is the wrong shape for it. Use the header and footer tool instead: the text sits in the margin where it belongs, stays fully readable, and does not interfere with the content. Watermarks are for marks that should cross the page. Everything else belongs in the margin.