When to Watermark a Document
A watermark communicates the status or ownership of a document at a glance. Marking a circulated file DRAFT stops anyone mistaking it for the final version; CONFIDENTIAL signals how it should be handled; a company name or "COPY" discourages a shared file from being passed off as an original. Because the mark sits across the page content rather than in a corner, it's visible on every printout and screenshot — which is the whole point.
How the Diagonal Watermark Is Applied
The tool draws your text across the centre of each page at a 45-degree angle, automatically sized to span the page's diagonal so it reads clearly on any page dimension. An opacity slider lets you set how bold or subtle the mark is — light enough to keep the underlying text readable, or strong enough to dominate. Every page in the document receives the same stamp, and the whole job runs in your browser with no upload.
Thai and other non-Latin watermark text is supported: the Noto Sans Thai font is embedded automatically when Thai characters are present.
A Watermark Is Not Encryption
It's important to know what a watermark does and doesn't do. It is a visual deterrent — a determined person could still read the text underneath, and image editors can attempt to remove it. If you need to actually prevent unauthorized people from opening the file, combine the watermark with the Protect PDF tool, which encrypts the document behind a password.