Can I put the watermark behind the page content instead of on top?

No - it is always drawn over the existing content, which is why the opacity slider is the control that matters. At the default 20 per cent the text underneath reads through perfectly clearly, so the practical effect is the same as a background tint. If your watermark is obscuring the document, lower the opacity rather than looking for a layering option.

Can I watermark only certain pages, or change the colour and position?

The watermark goes on every page, in mid-grey, diagonally across the centre - the wording, opacity and font size are what you control. To stamp only part of a document, split the PDF, watermark the section you want, then merge the pieces back together in order. Both of those tools also run in your browser, so the round trip takes about a minute.

Does adding a watermark stop people copying or editing my PDF?

No. A watermark is ordinary page content, so anyone with a PDF editor can remove it, and it places no restriction on copying, printing or editing. It is a deterrent and a label, not a lock - its value is that it survives forwarding, printing and screenshotting, so a leaked copy still says who it was for. Genuine restrictions come from password protection and permission flags, which are a different mechanism.

How to Add a Watermark to a PDF

You are sending a contract out for review, circulating a report that is not final, or handing a proposal to a client - and you want every page to say so. A watermark does that: faint diagonal text across each sheet, hard to lose in a forward or a printout. This guide covers what a PDF watermark really is, how to pick the opacity and size, and what it does not protect you from.

What a watermark actually is inside a PDF

Despite the name, a watermark is not a property of the file or a security setting you switch on. It is simply more content drawn onto each page - a line of text, angled, in a pale grey, layered over whatever was already there. To the file format it is no different from a heading or a caption.

That has two consequences. It sits on top of your content rather than behind it, so at a high setting it genuinely obscures the text underneath - which is why opacity matters. And it is real text, not a picture: crisp at any zoom, almost free in file size, and visible if someone selects the whole page or runs a search.

How to add a watermark to a PDF

Open the Watermark PDF tool in your browser.
Drag your PDF onto the page. The file name, size and page count appear, so you can confirm the right document loaded.
Type your watermark text. It starts on CONFIDENTIAL - replace it with whatever you need.
Set the opacity and font size with the two sliders.
Click Add watermark and download. Your browser saves the result as watermarked.pdf.

The text is stamped across the centre of every page, running diagonally up from lower-left to upper-right at 45 degrees in mid-grey bold Helvetica. Your original file is never modified - what you get is a new copy.

Choosing the opacity

The opacity slider runs from 2 to 100 per cent and starts at 20. It sets how strongly the grey shows against the page:

10-20 per cent is a light tint: the document reads normally and the watermark registers as background texture.
25-40 per cent is unmissable without fighting the body text. The sweet spot for a DRAFT or CONFIDENTIAL stamp.
60 per cent and above competes with the content, and near 100 it is a solid grey band - worth it only for a specimen copy, meant to be looked at but not used.

If unsure, err light and open the download to check. Each run starts again from the file you loaded, so repeated attempts never stack one watermark on another.

Choosing the font size: a worked example

The size slider runs from 20pt to 120pt, starting at 60pt. Longer wording needs a smaller size: the text is centred and drawn outward, so if it is wider than the page the start of it falls off the edge.

Take the default on a standard A4 portrait page, about 595 points wide. In bold Helvetica the word CONFIDENTIAL measures about 7.44 times the font size, so at 60pt it is roughly 447 points wide - comfortably inside 595, and once rotated it sits neatly in the middle of the sheet. At the maximum 120pt it measures about 893 points, far wider than the page, and the first letters are cut off on the left. For that word on A4 the limit is around 80pt.

A rough rule for A4 portrait: divide 595 by 0.7 times the number of characters and stay at or below the answer. A five-letter DRAFT tolerates anything the slider offers; a twenty-character phrase like SAMPLE - DO NOT COPY needs about 40pt. Shorter is better regardless - a sentence shrunk to fit reads as clutter, while one or two words at 60pt read as a stamp.

What to write on it

CONFIDENTIAL - the default, for anything that should not be forwarded on.
DRAFT or NOT FINAL - so last month's version is never mistaken for the signed one.
SPECIMEN or SAMPLE - for templates and example documents.
A recipient's name or company - the standard way to trace a leak, since each copy carries the name of who received it.

Keep to Latin characters. The watermark uses a font built into the PDF standard, which covers the usual Western European set - accented letters like e-acute and u-umlaut are fine - but it cannot render Devanagari, Chinese or other non-Latin scripts, and asking it to fails with an error rather than producing the wrong glyphs.

A watermark deters, it does not protect

Worth stating plainly, because the word implies more security than it delivers. The watermark is ordinary page content, so anyone with a PDF editor can strip it out. What it does well is signal intent and survive the casual routes by which documents escape - a forwarded email, a printout, a screenshot. All of those carry the stamp.

Restricting what people can do with a document is a separate mechanism: an owner password and permission flags, the same ones that can be cleared with Unlock PDF. And if the content must not be extractable at all, no watermark achieves that - the answer is not to send the document.

Does it make the file bigger or worse?

Barely, and no. The font is a standard one that need not be embedded, so all that is added is a short drawing instruction per page - a couple of hundred bytes, or about 2.5 KB across ten pages. Quality is untouched, because nothing is re-rendered or re-compressed: scans stay as sharp as they were, existing text stays selectable, and links and form fields keep working.

Is it private?

Yes. Watermark PDF runs entirely in your browser: the file is read from your own disk, the text drawn in memory on your machine, the result handed back as a download. Nothing is uploaded and no copy is left on a server - which matters more here than for most tools, since the documents worth watermarking are the sensitive ones.

If something goes wrong

The file will not load. A PDF that demands a password before it will even display is genuinely encrypted. Open it with the password, save an unprotected copy, and watermark that.
The watermark is cut off at the edge. The text is too wide for the page at that size - shorten it or pull the font size down.
An error appears instead of a download. Check the text box for non-Latin characters.

Watermarking is usually the last step before a document goes out. Before it you might merge the sections together, reorder the pages, drop the ones you do not need or add page numbers; afterwards, compress it if it is going by email. To stamp only part of a file, split it first.

Add your watermark now

One or two words at 20-30 per cent opacity are usually all it takes for every page to announce what it is. Open Watermark PDF, drop your file in, type the text, set the sliders and download the stamped copy - free, private, and without your document leaving your device.

Frequently asked questions

Can I put the watermark behind the page content instead of on top?: No - it is always drawn over the existing content, which is why the opacity slider is the control that matters. At the default 20 per cent the text underneath reads through perfectly clearly, so the practical effect is the same as a background tint. If your watermark is obscuring the document, lower the opacity rather than looking for a layering option.
Can I watermark only certain pages, or change the colour and position?: The watermark goes on every page, in mid-grey, diagonally across the centre - the wording, opacity and font size are what you control. To stamp only part of a document, split the PDF, watermark the section you want, then merge the pieces back together in order. Both of those tools also run in your browser, so the round trip takes about a minute.
Does adding a watermark stop people copying or editing my PDF?: No. A watermark is ordinary page content, so anyone with a PDF editor can remove it, and it places no restriction on copying, printing or editing. It is a deterrent and a label, not a lock - its value is that it survives forwarding, printing and screenshotting, so a leaked copy still says who it was for. Genuine restrictions come from password protection and permission flags, which are a different mechanism.