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Example

Input

File: proposal.pdf (15 pages)
Text: CONFIDENTIAL, center, -45°, 30% opacity, 60pt, gray

Output

proposal-watermarked.pdf — diagonal 'CONFIDENTIAL' on every page

Note

Hangul is supported — when the text contains it, a subset font is fetched once and embedded (Latin-only text downloads nothing extra). Han characters, kana and emoji are out of coverage. Watermarks are baked into page content (not a separate layer) — removal requires a PDF editor.

Usage / FAQ

When to use

  • Mark confidential documents with 'CONFIDENTIAL' / 'INTERNAL'
  • Mark drafts with 'DRAFT' so they're not confused with finals
  • Stamp every page with company / product name
  • Mark sample / test PDFs with 'SAMPLE'
  • Add 'EDUCATION USE ONLY' or similar usage restrictions

FAQ

Q.Is the watermark permanent?
A.Yes — baked into the PDF's page content. A receiver with a regular viewer can't remove it. A professional editor (Acrobat Pro etc.) can sometimes separate it as a layer — for stronger guarantees you need additional measures.
Q.What about Hangul / CJK watermarks?
A.Hangul works. When your text contains it, a Hangul subset font (about 1.5 MB) is fetched once and embedded — Latin-only text downloads nothing extra. The output PDF only carries the glyphs you actually used, so it barely grows. Han characters, kana and emoji are still out of coverage.
Q.Image watermarks (logo PNG)?
A.Text only at the moment. Image watermarks are a planned follow-up — compose a logo PNG onto each page.
Fun facts

  • A PDF 'watermark' is really just extra drawText / drawImage commands per page. There's no 'watermark layer' in the PDF spec — even Acrobat's watermark feature draws directly into page content. That's why regular viewers can't separate it.

    ISO 32000-1

  • Opacity entered the PDF spec in PDF 1.4 (2001). Before that (PDF 1.3 and earlier) watermarks could only be 100% opaque — to not occlude content you had to use small fonts or corner placement.

    Wikipedia — PDF imaging model

  • Survival rate of watermarks through print/scan/reprint is a common citation in court filings. Rotation + semi-transparency + large fonts together also impair OCR text recognition — a 'copy-tracking PDF' pattern.

    Wikipedia — Digital watermarking

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