PDF Watermark
Overlay a line of diagonal text on every page, such as "For internal use only" or "CONFIDENTIAL".
Drag in a PDF, or Choose file
Processed locally · No uploadPDF's standard fonts (Helvetica) contain no Chinese glyphs. Writing Chinese requires embedding a Chinese font file (several MB), which would balloon the output size — so this is limited to English letters and digits.The watermark is overlaid on the page, so anyone with an editing tool can remove it, it only guards against accidental sharing, not deliberate tampering.
When to use it
- You're sending a quote, résumé, or draft to a client and want it marked DRAFT or CONFIDENTIAL so it isn't mistaken for the final version.
- Internal training material or an unapproved proposal needs a visible source label on every page without obscuring the body text.
When not to
- You need real leak or tamper protection — the watermark is an ordinary text layer that can be selected and deleted, or cropped away, in any PDF editor.
- You want Chinese or Japanese text — the standard font has no CJK glyphs, so only ASCII letters, digits, and punctuation work.
Watermarks are overlaid locally by pdf-lib; the PDF is never uploaded and is cleared when you close the tab. Limits: English letters, digits, and half-width punctuation only (HelveticaBold has no CJK glyphs); one centered diagonal line per page, with no page selection or tiling; the watermark can be edited or deleted; encrypted PDFs can't be read. The source PDF is never modified.
Frequently asked
Why can't I use Chinese or Japanese in the watermark?
The built-in HelveticaBold is a PDF standard font with Latin glyphs only. CJK text requires embedding a font file, usually several megabytes, which would inflate every output; the tool keeps files small by accepting printable ASCII (letters, digits, half-width punctuation) only. For CJK, add an image watermark in a desktop editor.
Can the watermark be removed?
Yes. It's a single line of text added to each page's content, not encryption or a flattened image, so any PDF editor can select and delete it, and cropping the page removes it too. It discourages casual misuse, not a determined recipient. The original file is untouched and the output only grows slightly.
What opacity and angle should I use, and why doesn't the font scale with the page?
Defaults are 18% opacity, 45°, and 48 pt. 10–25% keeps the body readable while still visible; above 40% starts to obscure the page, and below 10% may vanish in print. Font size is absolute points and doesn't scale with page size, so A3 or large-format pages may need 72–120 pt.