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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

Currently the safe character set is ASCII (Helvetica Bold). Non-Latin scripts (Hangul, CJK) need a font embed and are a follow-up. 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.ASCII (Helvetica Bold) only for now. Non-Latin scripts need a font embed and are a follow-up — ASCII / digits recommended.
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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