How to Add a Watermark to a PDF (and What It Actually Protects)

A DRAFT or CONFIDENTIAL stamp across every page does something a covering email can't: it stays on the document after the document has been forwarded, printed, or pasted into someone else's slide deck. Adding one to a PDF takes a single step, and it leaves the text underneath exactly as it was.

What gets stamped

Upload the PDF, type the words you want, download it back. Your text is drawn diagonally through the middle of every page in bold grey at around 20% opacity — solid enough to read at a glance, faint enough that the paragraph it crosses is still legible. It sits on top of what's already there, so nothing in the original is moved, resized, or removed.

Keep the wording short

The type size is worked out from how many characters you type, so the length of your text is really a choice about how the page will look:

• One or two words — DRAFT, CONFIDENTIAL, SAMPLE — stretch nearly corner to corner. This is what the stamp is tuned for.
• A short phrase like a company name, a client name, or NOT FOR DISTRIBUTION still reads clearly at a glance.
• A whole sentence gets shrunk to fit the diagonal and ends up small enough to overlook, which defeats the point of stamping it.

If the message needs a sentence, put that in the email and keep the stamp itself to the shortest phrase that carries the meaning. Script isn't a constraint: Chinese, Japanese, Korean and Vietnamese all stamp properly, and full-width characters are measured as they'll actually be drawn, so a short Chinese phrase fills the diagonal without running off the page. Type something no font on the server can draw — an emoji, say — and you'll be told, instead of being handed a PDF full of empty boxes.

A watermark marks a document, it doesn't lock it

These two jobs get confused often enough to be worth separating. The stamp is ordinary page content laid over the top. It doesn't stop anyone opening the file, and it doesn't stop them selecting and copying the text underneath it. Someone determined can strip it, too — it's a single object on each page, and any real PDF editor can delete it.

What a watermark does well is tell an honest reader what they're holding, and make a casual forward feel like a decision. If you need something firmer, choose by what you're actually worried about:

• People opening the file at all — set an open password, so the PDF can't be read without it.
• Specific content being read — redact it. Redaction takes the underlying text out rather than covering it up, which a watermark never does.

Common questions

Can I stamp my logo instead of text?

Not with this tool — it stamps one line of text and nothing else. For most documents the company name typed out works as well as the logo would, since the point of a watermark is to be read rather than admired. If you specifically need artwork on every page, that's an image overlay, and it's a different job than this.

Will the watermark show up when the PDF is printed?

Yes. It's merged into the page itself rather than attached as an annotation or a comment, so it prints as it looks on screen and there's no viewer setting that hides it. The same holds if the pages are turned into images later — the stamp is part of the page by then, so it comes along.