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Put COPY, CONFIDENTIAL or your own words across every page, once in the middle or repeated, faint or strong. The file is handled inside your browser and not sent anywhere.
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The watermark is drawn onto every page as a see-through picture of your text. Everything else in the file stays as it was. A watermark marks a copy; it does not stop anyone from editing the file.
The PDF is read and written inside your browser by pdf-lib, and the preview is drawn there by pdf.js, the PDF reader built into Firefox. There is no upload step and no server route; the result goes straight to your downloads.
Your browser draws the text with the fonts already on your device, as a picture with a clear background, so it can be in Korean, Japanese or any other script without a font being added to the file. The picture is stored in the PDF once and drawn on every page at the strength you chose, so a long file grows only a little.
Because it is a picture, the watermark is not picked up when someone searches or copies the page's text; the original text still searches and copies as before. The rest of the file — links, fillable forms, bookmarks — is saved as it was.
“Once, in the middle” lays the text along the page's diagonal, or level, and sizes it to the page, so a landscape page and a receipt both get a mark that fits. “Repeated” covers the page in rows of smaller marks, offset like bricks. Either way the position is worked out on the page as you see it, so a scanned page turned on its side is marked the right way up.
A watermark says what a copy is for. On a copy of an ID card or a certificate, writing who it was given to — “for ABC Bank only” — makes it hard to reuse elsewhere. It does not lock the file: anyone with a PDF editor can still change or remove what is drawn.
A PDF with a password or restrictions cannot be written, so it is sent to Unlock a PDF first. The text can be up to 40 characters. The letters take the look of your device's fonts, so the same words may look slightly different on another computer.
No. The file is read, shown and saved inside your browser; this tool has no server step. To draw some pages the preview may fetch character maps or fonts from this site, never your file.
Yes. The text is drawn with your device's own fonts, so any script your device can show works, and no font is added to the file.
No. It marks the copy and says what it is for, but anyone with a PDF editor can still change or remove it. It does not add a password either.
PDF drawing: pdf.js (Apache-2.0) · PDF writing: pdf-lib (MIT)