PDF Watermark

Watermarking a PDF means drawing text or graphic on top of every page so the document carries an unmissable visual signal everywhere. The classic use is 'CONFIDENTIAL' or 'DRAFT' diagonal across the page — anyone glancing at any page sees the mark, anyone screenshotting one page sees the mark, anyone printing the document gets the mark on paper. The mark survives the casual ways content travels.

This tool adds a text watermark to every page of a PDF in your browser. Drop a PDF, set the text and styling, get a watermarked copy back. The output is a standard PDF that opens correctly in every viewer.

The implementation uses **pdf-lib** to draw text onto each page's content stream. The text becomes part of the page's drawing operations, alongside the original text and graphics. PDF viewers render it in the same compositing pass as everything else — there's no separate watermark layer that can be toggled off, no hidden 'real' page underneath.

**Positioning options.** Four standard placements cover the everyday cases:

- **Diagonal across the page** — the stock-photo-watermark layout, rotated -45° by default, centered on the page. The right pick for 'CONFIDENTIAL' / 'DRAFT' on documents that will be screenshotted, copied, or shared. The rotation makes the mark hard to crop out without losing significant content. - **Center horizontally** — non-rotated centered text. Useful for short marks like 'DRAFT' that don't need to dominate. - **Top of page** — a header-style mark that sits at the top of every page above the content. Good for less-intrusive marks that still ensure every page is identifiable. - **Bottom of page** — a footer-style mark. The most polite option; doesn't interrupt the reading experience but still ensures every page is marked.

**Styling.** Color picker for any hex value (the default `#999999` gray works well for low-contrast subtle marks; brighter colors like red work for harder warnings). Font size slider from 12 to 200 px. Opacity slider from 0 to 1 (the default 0.2 is barely-there subtle; bump higher for documents with busy content that would swallow a faint watermark). Rotation slider in diagonal mode from -90° to +90°.

**Font.** Helvetica Bold from the PDF spec's standard 14 fonts. These fonts don't need to be embedded in the output — every PDF viewer has them built in, which keeps the output file size identical to the input (within rounding). Custom fonts (your brand's typeface, a non-Latin script font) would require font-file embedding, which is outside this tool's scope; for that, a desktop PDF editor with font management is the right tool.

**One watermark, all pages.** This tool applies the same watermark to every page in the document. Per-page control (e.g., 'CONFIDENTIAL' on internal pages, 'PUBLIC' on the cover) is a different operation that mostly doesn't come up in practice — a single mark covers nearly every use case.

**Quality and file size.** Adding a watermark adds a few hundred bytes per page (the text drawing operations) plus the embedded font reference. A 100-page PDF gets watermarked with a file-size increase of maybe 30 KB. The visual quality is vector text — sharp at every zoom level, infinitely scalable.

**What watermarks are good for and what they aren't:**

- **Good for:** confidentiality marking, source attribution, draft / non-final indication, brand presence, distinguishing a watermarked-for-display copy from the clean PDF you keep for archival. - **Not good for:** real anti-tampering security (a PDF editor can strip the watermark in minutes), digital signatures or non-repudiation (use real cryptographic signing for those), forensic tracking (per-recipient marks require a batch workflow this tool doesn't offer).

**Limitations worth knowing.**

- **Text watermarks only.** No image watermarks (e.g., embedding a 'CONFIDENTIAL' image or your brand logo) in this version. pdf-lib supports image embedding; the UI just doesn't expose it. If demand is high, a separate image-watermark mode could be added. - **No per-page targeting.** Every page gets the same mark. - **No removal feature.** This tool only adds watermarks; removing them from a PDF you have but didn't create requires a PDF editor. - **Encrypted PDFs aren't supported.** Decrypt externally first.

**Privacy.** pdf-lib runs in your browser. The PDF is loaded into memory via the File API, watermarked, and downloaded as a blob URL. There's no network traffic during operation. Verify in DevTools by watching the network panel stay empty. Your sensitive document is exactly that — sensitive, and not uploaded.

**Edge cases handled:** very long watermark text (overflows the page width if you make it too long, which is on you); zero-opacity watermark (technically valid, produces an invisible mark — useful for testing the pipeline without visual change); very large font (50+ px takes most of the page width, which is fine for diagonal mode); 90° / -90° rotation (vertical text); empty watermark text (treated as no-op).