How to add a diagonal text watermark to a PDF
Drop in a PDF, type the watermark text (ASCII letters, digits and half-width punctuation only), set the size, opacity and angle, and the tool writes one centred diagonal line onto every page as a new watermarked.pdf. The original file stays untouched and nothing is uploaded.
When a watermark actually helps
A watermark is a communication device, not a security control. When you send a quote, a CV or a draft proposal for review, a visible DRAFT or CONFIDENTIAL line reduces the chance that a screenshot gets treated as the final version.
Internal training material, unpublished documents and anything that needs a source marker on every page fall into the same category. The watermark only has to be legible and stay out of the way of the body text.
- Sending preview copies to clients marked DRAFT, SAMPLE or CONFIDENTIAL
- Circulating unfinished internal documents with a department or date marker
- Sample submissions where the file should not pass as a final version
Settings that avoid surprises
Only ASCII characters are accepted: Latin letters, digits and half-width punctuation. The reason is practical — the tool uses the PDF standard font Helvetica, which has no CJK glyphs. Writing Chinese or Japanese requires embedding a font file that is usually several megabytes, and every output would grow accordingly.
Opacity of 10–25% is the usual range: below 10% the mark may vanish in print, above 40% it starts to interfere with reading. A 45° angle is the common diagonal. Font size is an absolute point value and does not scale with the page, so 48 pt looks small on A3 or a large artboard — 72–120 pt suits bigger formats.
- Start with a short English phrase: DRAFT, CONFIDENTIAL, INTERNAL USE ONLY
- Begin around 18% opacity; for print, err on the lighter side
- Increase the size for large pages, or the mark will look tiny
- Keep a copy of the original — the tool writes a new file
Limits, and stricter alternatives
The watermark is a line of text drawn onto the page content. It is not encrypted and not rasterised, so any PDF editor can select and delete it, and cropping the page removes it too. It discourages accidental forwarding; it does not stop a determined person.
If the goal is genuinely confidential, use permission passwords, digital signatures, per-recipient serial numbers, or send flattened images instead. For Chinese watermarks, tiled patterns or a different string on each page, desktop layout software or a small script is the better tool.
- Tamper resistance: digital signatures, permission passwords, read-only distribution
- Chinese or tiled watermarks: desktop software or a script
- Per-page serial numbers: generate per page, then merge
FAQ
Why can't I write a Chinese watermark?
The tool uses Helvetica, a PDF standard font with no CJK glyphs. Displaying Chinese requires embedding a CJK font file, typically several megabytes, which inflates every output. Only ASCII letters, digits and half-width symbols are accepted. For Chinese, render a PNG watermark in an image tool and overlay it as an image instead.
Can the watermark be removed afterwards?
Yes. It is a text line drawn on the page, not encrypted and not flattened, so a PDF editor can select and delete it, and cropping the page also removes it. It signals intent; it does not prevent tampering. Pair it with a permission password or a digital signature when protection matters.
What opacity and angle should I use?
A common choice is 10–25% opacity at 45°. In that range the mark is visible without fighting the text; above 40% it interferes with reading, below 10% it may disappear in print. Angles of 30° or 60° also work — just keep them consistent across the document.
Related tool：PDF Watermark