Watermark a PDF

Mark a document as a draft, label it confidential before it circulates, or put your name across a portfolio. The text is drawn over the existing page content as real, selectable text — the page underneath is left exactly as it was.

How to use it

1. Open the Watermark PDF tool and drop in your document.
2. Type the text you want stamped across the pages.
3. Set the opacity, colour and layout — or keep the defaults.
4. Watermark, then download the marked-up PDF.

What a watermark is actually for

A watermark communicates the status of a document to whoever is holding it. "DRAFT" across a contract stops someone signing a version that was never final. "CONFIDENTIAL" reminds a recipient not to forward it. A name or company across a portfolio makes an unattributed copy obviously unattributed.

It is worth being clear about what it is not: a watermark is a deterrent and a label, not a security control. Anyone determined enough can remove one, and slimdocs makes no claim otherwise. If a document genuinely must not be read by the wrong person, encrypt it with the Protect PDF tool — that is the tool that actually restricts access.

Getting the opacity right

The tension in every watermark is between being noticed and being in the way. Too faint and it does not register; too solid and the document becomes hard to read, which defeats the point of sending it.

Around 15–20% is the sweet spot for most documents — clearly visible as a label, but the text underneath reads without effort. Go a little heavier for something you actively want to discourage people from using, such as a proof or a sample. Go lighter on pages that are already dense with tables or figures, where any overlay competes with real content.

Size and layout are handled for you

By default the text is drawn diagonally, corner to corner, and sized to span about 80% of the page. That is calculated per page from the actual page dimensions, so an A4 portrait page and a US Letter landscape page in the same document each get a stamp that fits properly rather than one overflowing and the other looking lost.

Diagonal placement is the conventional choice because it crosses the body text without sitting on any single line, and it is hard to crop off. The horizontal option is there for documents where a diagonal band would obscure something important, such as a wide table or a full-page image.

The page underneath is untouched

The watermark is a new drawing operation added on top of the existing page content. Nothing in the original is removed, rewritten or flattened — text stays selectable, links keep working, and vector graphics stay sharp at any zoom.

One consequence worth knowing: because the original content is still there, the watermark sits over it rather than being fused into it. That is the correct behaviour for a document you want to remain usable, and it is the reason a watermark should never be mistaken for redaction. To remove information from a PDF you must delete it, not cover it up.

Marking only some pages

The page selection box takes the same 1-based lists and ranges as the other PDF tools — "1" for a cover page only, "2-10" for a range, or blank for the whole document. Watermarking just the first page is a common choice for a report where the cover carries the status and the body should stay clean.