What this does

This stamps text or an image onto the pages of a PDF — once per page or tiled across the whole thing, at any angle and any opacity, and either over the content or underneath it. The file is edited in your browser and never uploaded, which matters here more than on most tools: the documents people watermark are contracts, drafts and proofs.

Over or under

This is the option most watermark tools don't give you, and it's the one that decides whether the result is usable. A mark drawn over the content sits on top of the words, so a paragraph under a big diagonal “CONFIDENTIAL” is read through it. A mark drawn underneath is covered by the text, so the page reads normally and the watermark shows through the white space around it.

Over the top is the default, and there's a blunt reason for it: underneath only works on pages that don't paint their own background, and a great many PDFs do. Word, Acrobat and most scanners lay down a white rectangle before anything else, and a mark drawn beneath that rectangle is not faint — it is gone. At the opacities a watermark is set at, over the top costs you almost nothing in readability and always shows.

Underneath is still there, and it's the nicer result when it works: the text stays completely crisp. There is no reliable way to ask a PDF whether it paints its own background — a white rectangle is just another filled path — so instead of guessing, the preview stamps page one and compares it against the untouched page. If not a single pixel moved, you're told the mark is hidden rather than left to find out after downloading it.

Once, or tiled

A single mark is the classic: one diagonal stamp across the middle, or a small notice in a corner. Tiled repeats the mark edge to edge with alternate rows offset, so it covers the page evenly and can't be cropped off. Tiling is what you want when the point is to make a document awkward to reuse rather than simply to label it.

How to use it

Drop in a PDF.
Type your text, or choose a PNG logo.
Set the angle, opacity and position — the preview updates as you go.
Add the watermark, and download.

Things worth knowing

Underneath only works on some PDFs. A page that paints its own background — which Word, Acrobat and scanners all do — hides anything drawn beneath it completely. Over the top always shows, which is why it is the default.
A watermark is not security. Anyone with the right software can take it off again, and if it's drawn underneath the content it can be removed without touching the text. It marks a document; it doesn't protect one.
Text uses the fonts built into PDF. Those cover Latin-1 — English, French, German, Spanish, the accents and the curly quotes — and nothing beyond it. For Chinese, Greek, Arabic or an emoji, use an image watermark instead. You'll be told which characters are the problem rather than handed a broken file.
Images have to be PNG or JPEG. Those are the two a PDF can carry directly. A PNG keeps its transparency, so a logo sits on the page rather than in a white box.
Pages already turned are handled. A scan saved sideways carries a rotation flag, and a watermark laid out against the numbers in the file rather than the page you see would come out down the wrong axis. This lays out against the page as displayed.
Everything else in the file is left alone. The pages are edited in place rather than copied into a new document, so bookmarks, links, form fields and metadata all survive exactly as they were.

Frequently asked questions

Is my file uploaded?

No. It's read and edited in your browser. You can watch the network panel while it runs, or disconnect from the internet once the page has loaded and watermark anyway — it still works.

Why can't I see my watermark?

Almost certainly because Underneath the page's content is on and the page paints its own background — a white rectangle, a full-page photograph, a scanned image. The mark is there, underneath all of it, and nothing shows. Turn that option off and it will appear. The preview says so when it happens.

Can I watermark only some pages?

Yes — put a range in the Pages box, like 1 for a cover sheet or2- for everything after it.

Can I remove a watermark with this?

No. This adds one. Taking an existing watermark out of someone else's PDF is a different job and not one this site does.