How to Watermark a PDF (and What a Watermark Does Not Do)

You have a document you are about to send somewhere it might travel further than you intended. A contract going to a client. A draft going to three reviewers. A bank statement going to a landlord. You want it to say CONFIDENTIAL, or DRAFT, or just your own name, so that wherever a copy ends up it still says where it came from.

That is what a watermark is for. This guide covers how to put one on every page of a PDF without uploading the document anywhere, why the stamp comes out sideways on so many scanned files, and the one thing people get wrong about watermarks that actually matters.

A watermark labels a document. It does not protect it.

Start here, because everything else in this guide is easier once this is clear.

A watermark is drawn on top of the page. The text underneath it is still there. It can still be selected, copied, searched and extracted. Anyone who opens the file in a PDF reader, selects all and pastes into a text editor gets the entire document — the stamp comes along for the ride as one more line of text.

So if you are watermarking a document to stop someone reading a figure, an account number, a name or a medical detail, a watermark does nothing at all. That job is redaction: removing the content from the file so it is genuinely no longer there. The two are different operations, they are done with different tools, and confusing them is how people end up emailing a statement they believe they have protected.

Use a watermark to say what a document is and where it came from. Use redaction to remove something. Use a password to control who opens it. They are three separate jobs.

How to watermark a PDF in the browser

The fastest route, and the only one where the file never leaves your computer, is the Add Watermark to PDF tool. There is nothing to install and no account to make.

1. Open the PDF. Drag it onto the page or use the file picker. You can add several documents at once — the settings apply to the whole batch.
2. Type the watermark text. CONFIDENTIAL is the default. It can be a client name, a case number, a date, a URL, an email address — anything up to about 120 characters. Beyond that it stops reading as a watermark and starts reading as body text.
3. Choose the layout. Repeated across the page, one stamp across the middle, or one stamp at the foot. The trade-off is below.
4. Set opacity and size. The default is 12% opacity and 44 pt, which is visible at a glance without obscuring the text you still need to read. A watermark that makes a contract unreadable is not doing its job either.
5. Download. Each document comes back as name-watermarked.pdf, or take the batch as a ZIP.

Everything happens in your browser tab. Nothing is uploaded, there is no queue on a server, and the page keeps working if you disconnect from the internet — which is the simplest way to satisfy yourself that it is true.

Tiled or centred? The honest trade-off

Most tools give you one centred stamp and stop there. That is the version that is easy to remove: open the file in an editor, delete one object, done. If the point of the watermark is that it survives, one stamp does not do much.

Tiled repeats the text diagonally across the whole page. Removing it means editing most of the document, and painting over one copy leaves a dozen others visible. This is the right choice for anything you are sending out of your own control.

Centred puts one stamp across the middle of the page. It is clean, it is legible, and it is the right choice when the watermark is for the reader rather than for the recipient — a draft you want your own reviewers to notice, a template that should not be mistaken for a final version.

Footer keeps the label out of the way entirely: one small line at the foot of each page. This is what you want for a document that is watermarked for provenance rather than for warning — a name, a date, a job number.

Why your watermark came out sideways

This is the failure that sends people looking for a different tool, and it has nothing to do with the tool being cheap or new.

A scanned page is usually not stored the way you see it. The scanner records a landscape image and adds a rotation instruction to the page telling the viewer to turn it 90 degrees. Your PDF reader honours that instruction, so the page looks upright and everything is fine.

Now a tool draws a watermark. If it draws the text in the page's own coordinate system without accounting for that rotation instruction, the text is drawn upright relative to the stored page — which means the viewer then rotates it along with everything else, and the watermark appears running vertically down the side of the document, reading bottom to top.

It is a small piece of arithmetic: work out where the stamp goes in the orientation the reader actually sees, then map that back through the page's rotation before drawing. Getting it right means the watermark reads horizontally on pages rotated 0, 90, 180 and 270 degrees. Getting it wrong is invisible on the documents most people test with, which is why it survives in shipping tools — you only see it on the scans.

The tool here does the mapping for every page individually, so a document that mixes an upright cover sheet with sideways scans comes out correct throughout. If a page in your PDF is rotated and you would rather fix the file than work around it, the Rotate PDF tool handles that separately.

What the desktop routes actually produce

Worth knowing if you already have one of these open.

• Microsoft Word will watermark a document, and it is a real watermark — but it is a WordArt object in the header, and it only exists once you export to PDF. If you only have the PDF, you cannot watermark it in Word without rebuilding the document. Word's export also re-renders the pages, so a scan inside it loses a generation of quality.
• Adobe Acrobat has a proper watermark feature with the best controls of the three, and it costs a subscription. It works on the PDF directly without re-rendering.
• macOS Preview has no watermark tool. The usual workaround — adding a text box in Markup — puts the stamp on one page only, and it becomes part of the page content rather than a layer you can remove later.

The online tools are a mixed bag. Many upload your file to a server to stamp it, which is a poor trade for exactly the documents people watermark: the reason you are labelling a contract CONFIDENTIAL is that you do not want copies floating around, and the first thing you did was send a copy to a stranger's server. Others work in the browser but only offer a single centred stamp, or fail on rotated pages, or produce a document that will not open at all.

The awkward cases, and what should happen

A tool is judged by what it does when the input is not a clean 10-page A4 report. Here is what this one does, so you can check it against your own file:

• Password-protected PDFs are refused, by name. Not because it is hard, but because it is impossible to do correctly: a protected file stores its page content encrypted, and a new layer added on top would be plaintext inside a document that claims to be encrypted — which is a file no reader will open. Remove the password, watermark it, then protect it again.
• A non-PDF is refused by name. Renaming a Word document to .pdf does not make it one, and the tool says so rather than producing an empty file.
• Mixed page sizes are laid out per page. A document with an A4 page, a landscape photograph and a narrow bookmark gets a layout that fits each one, rather than one stamp positioned for the first page and running off the edge of the others.
• Non-English text is refused with a reason. The PDF standard fonts cover Western European characters only. A Cyrillic, Greek, Arabic or CJK watermark needs a font embedded in the file. Rather than producing a page of blank boxes, the tool tells you what the limitation is.
• Your metadata is left alone. The document's own author, title and producer fields are not overwritten by the tool. The original page content, fonts and images are carried through untouched — only the pages you stamp change, and only by gaining a layer. If the author field itself is the problem, that is a job for the metadata remover for images, or Acrobat's document properties for a PDF.

Watermarking a whole folder of documents

Legal and administrative work rarely involves one file. A bundle to be stamped with a case reference, a set of statements to be marked with the sender's name, a batch of drafts to be labelled before circulation.

Drop them all in at once. The settings panel belongs to the batch, so the text, layout, opacity and size you choose apply to every document, and each one is stamped and saved under its own name with -watermarked appended. Download them individually or take the whole set as one ZIP.

If the files are too large to send afterwards, the PDF compressor will bring them down — again without uploading anything.

The short version

A watermark labels a document. It does not hide anything, and it does not stop anyone reading the text underneath — that is redaction, and it is a different tool. Use a watermark to say what a document is and where it came from, and use it on documents you would rather not hand to a website: contracts, statements, medical letters, unpublished work.

Choose tiled if the watermark needs to survive, centred or footer if it just needs to be seen. Watch for sideways stamps on scanned pages, which means the tool is ignoring the page's rotation. And keep the opacity low enough that the document is still readable, because a watermark nobody can read past has failed too.

Watermark your PDF in the browser — every page, any rotation, and the file never leaves your computer.