Add a Watermark to a PDF

No. The file is read into memory and stamped entirely in your browser with pdf-lib. Nothing is sent to a server, so confidential and legal documents stay on your device.

One line of text, an opacity from 10% to 60%, a font size in points, a hex color, and either a flat 0 degree or diagonal 45 degree angle. The text is drawn in Helvetica Bold and centered on the page.

Yes. The same stamp is centered on every page in a single pass, and there is no per-page configuration. It is applied identically whether the document has one page or hundreds.

Two presets: Flat (0 degrees) lays the text horizontally, and Diagonal (45 degrees) runs it from the lower left toward the upper right. The diagonal is the classic look because it crosses the most content. Arbitrary angles are not offered in the tool.

A CSS hex color like #888888 or the shorthand #f0a. Anything the field cannot parse falls back to a neutral gray rather than failing, so a stray keystroke never breaks the stamp.

Font size is clamped to a sane 8 to 200 point range and rounded to a whole point. A tiny or huge value, or an empty field, is pulled back into that range so the watermark stays readable and on the page.

Not in one click. It is drawn into each page's content stream, not kept as a separate toggleable layer. It marks a document for its readers; it does not encrypt, lock or otherwise secure the file.

If the PDF opens without a password in your viewer, it will watermark here. Files that demand a password just to open cannot be processed, and a broken or unreadable PDF shows a clear error instead.

The tool inserts a -watermarked suffix before the extension, so report.pdf downloads as report-watermarked.pdf. Your original file on disk is untouched.