What watermarks are used for
A watermark labels a document at a glance. “DRAFT” stops an unfinished version being mistaken for the final one, “CONFIDENTIAL” signals handling rules, “COPY” distinguishes a duplicate from an original, and a logo marks where a document came from. Because the mark sits on every page, it travels with the document even if individual pages are copied out.
Text and image watermarks
For a text watermark, type your wording and choose its size and color. For an image watermark, upload a PNG or JPG — a logo, stamp, or seal — and choose how large it appears relative to the page. Both types let you set opacity and rotation; the default is a diagonal, semi-transparent mark at −45°, which stays readable without hiding what is underneath.
The watermark is centered on every page and drawn over the existing content. For a text watermark, characters outside the standard Latin set (for example Chinese or Arabic letters) cannot be rendered by the PDF font and are replaced with a question mark, so use an image watermark when you need other scripts.
Choosing settings that work
Keep opacity low — somewhere around 15–30% — so text underneath stays easy to read, and pick a light gray rather than a strong color. Use a larger font size for short words and a smaller one for longer phrases so the text fits across the page. On pages with dark photos, a light watermark may be hard to see, so check a few pages of the result before sending it.
What a watermark does not do
A watermark is a visible label, not a security feature. Someone determined can edit or crop it out, so do not rely on it to prevent copying — use Protect PDF if you need access control. The Remove Watermarks tool exists for the legitimate case of cleaning up your own documents. Watermarking runs in your browser, so your file is not uploaded.