PDF Watermark

What a watermark is for

A watermark marks a document's status or ownership: DRAFT, CONFIDENTIAL, a company name, a recipient's identifier. It is a deterrent and a label, not a security control. Anyone determined to remove it can, because it is simply content drawn on the page. Treat it as a way to stop honest mistakes, such as a draft being circulated as final, rather than as protection against a motivated actor.

Opacity and legibility

The tension is between a watermark being visible and the document remaining readable. Around 10 to 20 percent opacity is usually the right range for a large diagonal stamp behind body text. Above 30 percent it starts competing with the content; below 8 percent it disappears when printed on a low-quality printer. A diagonal angle of roughly 45 degrees covers more of the page than horizontal text and is harder to crop away.

Behind or in front

Placing the watermark behind the page content keeps text fully legible and is right for most documents. Placing it in front makes it harder to obscure and is right when the watermark is the point, such as a proof copy or an unpaid invoice. Behind-content placement fails on pages with a solid white background box, because the box hides the watermark entirely; if a scanned page swallows your watermark, that is why.

Per-recipient watermarking

Stamping each copy with the recipient's name is a genuinely effective deterrent against redistribution, because a leaked copy identifies its source. This works far better than a generic CONFIDENTIAL stamp, which nobody reads after the first page.

Removal is trivial for anyone who tries

Because a watermark is page content, it can be removed by editing the content stream, and automated tools exist for this. Do not rely on it to prevent copying. If a document genuinely must not be redistributed, control access to it rather than marking it.