Add a watermark to a PDF
Stamp a text watermark on every page of a PDF, for example «CONFIDENTIAL» or «DRAFT», diagonal and semi-transparent. Everything happens in your browser.
One PDF file
What a watermark is for
A watermark is text overlaid on the content, useful to mark a document as a draft, confidential or copy, to discourage its distribution, or to put your name on a piece of work before sharing it. Being semi-transparent and diagonal, it stays readable without covering the text underneath.
Tip
Keep the intensity low (around 20%) so it doesn't get in the way of reading. A bright color like red makes the text clearly visible; grey is more discreet and suits formal documents.
What a watermark is actually for
A watermark does not protect a document, it declares its status: «draft», «copy», «confidential», «not for sale». It exists to stop a provisional version being mistaken for the final one, which is the commonest accident when a file circulates by email.
The second use is traceability: putting the recipient's name on every page of a confidential document does not stop them forwarding it, but it makes plain whose hands it passed through. It is why circulating accounts and dossiers carry a personalised watermark.
It is not protection
It has to be said plainly: a watermark can be removed. It is a layer on top of the content, and anyone with the right tools strips or covers it in minutes; the text underneath stays intact and selectable.
If the document contains data that must not be read, a watermark is the wrong instrument: the right one is to redact the data properly, covering it and then removing the underlying text. A black rectangle drawn on top can be moved, and everything is still underneath it.
How to choose a readable watermark
An effective watermark is visible enough to read and faint enough not to cover the text: in practice a light grey at 10 to 30% opacity, on the diagonal, in a large sans-serif face. Bright red seems like a good idea and makes the printed document unreadable.
Watch out for black and white printing, where almost every document ends up: a grey that is too light disappears entirely and a saturated colour becomes a dark grey that swallows the words. Before distributing the file, one test print is worth ten previews.
Nearby tools
To really hide data there is Redact data on a PDF. If you need to sign or write on the document, look at Sign PDF and Write on a PDF.