Watermark a PDF

A PDF page has two sizes: the one written in the file, and the one you see. A page can carry a rotation of 0, 90, 180 or 270 degrees, and every reader applies it when drawing. A scanned landscape sheet is very often stored as a portrait page with a quarter turn on it.

Tools that stamp across the stored page get that wrong. On a page with a quarter turn, a 45 degree diagonal drawn in the file comes out at 135 degrees on screen, crossing the other way and hanging off the corners, and a flat watermark ends up running up the spine.

This tool works out where the watermark goes in the frame you actually see, converts that point back into the page's own coordinates, then adds the page's rotation to the text angle so the reader's turn cancels out. A file that mixes portrait and landscape scans comes out consistent, every stamp crossing at the same angle.

A 48 point watermark is a bold statement on a phone sized page and a small caption on an A0 poster, which is why the size here is a percentage of the page width instead. Sixty percent means the stamp spans roughly sixty percent of the sheet whatever the sheet is, so a report that mixes A4 pages with a landscape appendix stays consistent.

The margin is a hard limit on top of that. A long phrase turned to 45 degrees needs more room than the same phrase lying flat, because a turned box is wider and taller than the text inside it, so the size is reduced until the whole thing fits. That is why a very long watermark comes out smaller than the percentage you asked for.

A watermark is a label. It says draft, sample, confidential or not for distribution loudly enough that nobody circulates the file by accident, and it survives printing, screenshotting and being emailed on, which a note in a covering message does not.

It is not protection. The text is ordinary page content, so someone with a PDF editor can select it and delete it, and nothing drawn on a page can stop a camera. If the file genuinely must not be read by the wrong person, a watermark is the wrong tool. Use it to prevent mistakes, not to stop determined people.

Around 15 to 25 percent opacity is the sweet spot. Fainter than that and it disappears when the page is printed in greyscale. Darker and the text underneath becomes hard to read, which defeats the point of sending the draft at all.

Nothing existing is touched. The watermark is added as new content on top of each page, so text stays selectable, images are not re-compressed and the page count is exactly what it was. The tool says how many pages it stamped and how many the file still has, so you can check.

The typefaces are the ones built into every PDF reader, so nothing has to be embedded and the file grows by a fraction of a kilobyte per page. That is also why the wording is limited to Latin letters, digits and punctuation.

Related: add page numbers to PDF stamps numbers instead of a label, rotate PDF straightens a sideways scan for good, and merge PDF joins the parts together before you stamp the result. For pictures there is watermark image.

How do I add a watermark to a PDF for free?

Drop the PDF in, type the words you want stamped across it, set the angle, the size and how faint it should be, then save. There is no account, no upload and no page limit. The watermark is drawn into the file itself, so it prints and it survives being emailed on.

Is my file uploaded anywhere?

No. The PDF is opened by this page in your browser and the stamped copy is written there too, so the file never leaves your device. That is also why it keeps working when you go offline, and why a contract or a medical report is safe to run through it.

My PDF has sideways scanned pages. Will the watermark come out crooked?

No. A page carries its own rotation of 0, 90, 180 or 270 degrees, and this tool reads it, places the watermark in the frame you actually see on screen, then converts that position back into the page's own coordinates and turns the text to match. A 45 degree diagonal crosses every page at 45 degrees, whichever way the page was scanned.

Can I watermark only some of the pages?

Yes. Choose only these pages and type a selection such as 1-3, 7 or 4- to stamp from the fourth page to the end. Every other page is written out untouched, and the page count of the saved file is the same as the original.

Can the watermark be removed?

By someone determined, yes. A text watermark is ordinary page content, so a PDF editor can select and delete it. Treat it as a clear label saying draft, sample or confidential, not as a lock. Nothing that renders on a page can stop a screenshot.

Why is my watermark smaller than the size I asked for?

The size is a share of the page width, and the margin is a hard limit. A long phrase set to 90 percent and turned 45 degrees would run off the corners, so it is scaled down until the whole thing fits inside the margin. Shorten the text or drop the angle back towards zero and it will take the full size.

Can I use symbols or a non Latin script?

Not with these typefaces. The fonts built into every PDF reader cover Latin letters, digits and punctuation, which is what keeps the saved file the same size as the original. The tool says so before you save rather than failing at the end, so nothing is lost.

Does watermarking make the file bigger or blurry?

Neither. The text is added as new content on top of each page, so nothing existing is touched, images are not re-compressed and the text underneath stays selectable. The file grows by a fraction of a kilobyte per page.