PDF Watermark

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About the PDF Watermark Tool

The PDF Watermark Tool stamps a tiled diagonal text watermark across every page of a PDF — entirely in your browser via pdf-lib. Use it to mark documents as DRAFT or CONFIDENTIAL, add copyright notices, or embed reviewer initials before sharing externally. The watermark is rendered on top of existing content with configurable opacity, font size, rotation, color, and grid density. Files stay on your device — sensitive contracts and reports can be watermarked without exposing them to a third-party service.

Updated: May 8, 2026

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How to use the watermark tool

  • Drop a PDF file (up to 200 MB, 1,000 pages). The live preview panel renders the first page with your current watermark settings.
  • Configure the watermark text — pick a preset (CONFIDENTIAL, DRAFT, DO NOT COPY) or type a custom string.
  • Tune appearance: opacity (5-100%), font size, rotation (-90° to +90°), color (Gray / Red / Black / Blue presets or custom hex).
  • Tune layout: density (horizontal step 100-800 px, vertical step 50-500 px) controls how tightly the diagonal pattern tiles across each page; offset position fine-tunes X/Y placement.
  • Click Download — the watermark is composited above existing content and the result saves as `<original>_watermarked.pdf`.

Common use cases

  • Marking DRAFT or CONFIDENTIAL on contracts before circulating to reviewers.
  • Adding copyright notices to creative work before client delivery.
  • Stamping invoices as PAID, VOID, or REISSUED.
  • Embedding reviewer initials or timestamp on legal documents.
  • Branding outputs with a company logo before external distribution.

Privacy and security

pdf-lib runs as bundled JavaScript inside your browser. The PDF, the watermark image, and the stamped output all stay client-side — nothing is uploaded. This is critical for watermarking confidential documents that should not be exposed to a cloud SaaS provider before they are even authorized for distribution. Refreshing the page clears the loaded file; closing the tab removes it from memory.

Tips and pitfalls

  • Watermarks are visual only — they do not encrypt or restrict the underlying content. Anyone can extract the original page bitmap and remove the watermark with image-editing tools. For tamper-evident or rights-managed documents use PDF/A-2 + cryptographic signatures.
  • Opacity below 20% becomes nearly invisible on photo-heavy pages and may not survive printing. Test the rendered output at intended reproduction quality.
  • Diagonal text needs careful sizing — too large and it overflows page edges; too small and it loses readability. Default is 60° rotation at 50pt; adjust for your aspect ratio.
  • Image watermarks should be transparent PNG. JPEG backgrounds (white box around the logo) look unprofessional. PNG with alpha channel composites cleanly.
  • Batch watermarking multiple files runs sequentially in the browser. Large batches (50+ files) may take minutes and stress browser memory.

Frequently Asked Questions

Can I watermark every page or just the first?
Both. The default is "every page"; toggle "First page only", "Last page only", or specify a custom page range (e.g., 1-5, 10-12) to limit the watermark to those pages.
Does watermarking modify the original PDF?
No. The output is a new PDF; the original file you uploaded stays unchanged in your filesystem. The tool reads, watermarks in memory, and writes the output as a download.
Can the watermark be removed?
Yes — visually. PDF watermarks are just additional content layered above the original. Anyone with image-editing tools (Photoshop, GIMP) can crop, mask, or replace the page bitmap. For genuine tamper-evident documents, use PDF digital signatures or PDF/A-2 with cryptographic protection.
How transparent should the watermark be?
For DRAFT-style stamps, 30-50% opacity is the sweet spot — clearly visible without obscuring the underlying text. For background-only branding (subtle logo behind the text), 10-20% works. Always test the printed output if the document will be reproduced.
Does the watermark size scale with page size?
The font size you set is in points (1/72 inch), so it stays constant in physical size regardless of page dimensions. A 50pt watermark is the same physical size on A4, Letter, or A3. Adjust if your pages are mixed-size.
Can I batch-watermark many PDFs at once?
Yes. Drop multiple PDFs, configure the watermark once, and the tool applies it to all and downloads a ZIP of results. For 50+ files consider splitting into smaller batches to avoid browser memory pressure.
Are CJK or accented characters supported in text watermarks?
Yes — when you select a font that contains those glyphs. The default fonts (Helvetica, Times, Courier) cover Latin-1 only. Toggle "Custom Font" and upload a font (Noto Sans CJK for 한글 / 中文 / 日本語; Noto Sans Arabic for Arabic) to embed the necessary glyphs.
Is my PDF or watermark image uploaded?
Never. Both inputs and the generated output stay in your browser. The DevTools Network tab confirms zero outbound requests during watermarking.