CONFIDENTIAL, DRAFT, COPY — stamped on every page, without uploading the file
Need a logo or letterhead instead of text? Upload your own one-page stamp PDF:
| Stamp | Typical size | Opacity | Rotation | Layer | Notes |
|---|---|---|---|---|---|
| CONFIDENTIAL | 48 pt | 30–40% | 45° | Overlay | Must stay visible on any background |
| DRAFT / PRELIMINARY | 60 pt | 45–60% | 45° | Overlay | Loud on purpose — nobody should mistake it for final |
| COPY | 24 pt | 25–35% | 45° | Tiled 3 × 3 | File-copy control; survives cropping of one mark |
| DO NOT DISTRIBUTE | 28 pt | 35% | 30° | Overlay | Longer phrases read better at a shallower angle |
| Firm name / letterhead | 24 pt | 100% | 0° | Underlay | Bottom-stripe or margin placement; keep content readable |
| Date + recipient (leak tracing) | 14 pt | 50% | 0° | Overlay | Tiled pattern, small — identifies the leaked copy |
Sizes assume US Letter / A4 pages; scale up on Tabloid/A3 drawings. Opacity is the honest lever: below ~20% a mark prints faintly and photocopies away; above ~50% it starts fighting body text.
| Page size | Width × height (pt) | Width × height (in) | 45° diagonal |
|---|---|---|---|
| US Letter | 612 × 792 | 8.5 × 11 | 1,000.9 pt |
| US Legal | 612 × 1,008 | 8.5 × 14 | 1,179.2 pt |
| A4 | 595.28 × 841.89 | 8.27 × 11.69 | 1,031.1 pt |
| A3 | 841.89 × 1,190.55 | 11.69 × 16.54 | 1,458.1 pt |
| A5 | 419.53 × 595.28 | 5.83 × 8.27 | 728.3 pt |
| Tabloid (11 × 17) | 792 × 1,224 | 11 × 17 | 1,457.9 pt |
A diagonal watermark needs its text to span meaningfully less than the diagonal or it runs off the corners. CONFIDENTIAL at 48 pt spans 357.31 pt horizontally — 58% of Letter's width and 36% of its 1,000.9 pt diagonal, which is why the classic look works without clipping.
There's no "watermark" feature inside the PDF format — a watermark is just content drawn on every page. Tools differ only in where that content comes from and how it's applied. This one builds a single-page stamp PDF with your text (pdf-lib draws it at your size, color, opacity, and angle), then a qpdf WebAssembly engine stamps that page onto the pages you chose — on top of the content (overlay) or behind it (underlay). Same mechanism Adobe's background/watermark feature uses, running in your browser instead of their cloud.
Rotation happens around the text's baseline start point, not its center, so a naive "draw at page center" lands a diagonal stamp off-center and often clipped. The engine measures the text first — CONFIDENTIAL at 48 pt in Helvetica-Bold is 357.31 pt wide and 44.40 pt tall — then solves for the anchor point that puts the rotated text's center on the page's center: at 45°, that anchor sits 195.37 pt from the left and 253.97 pt from the bottom of a Letter page (306 − 110.63 and 396 − 142.02 in the text's rotated frame). Tiled mode runs the same solve around nine evenly-spaced centers.
Start with a 3-page Letter-size quarterly report, 1,848 bytes. The stamp: CONFIDENTIAL, Helvetica-Bold 48 pt, 50% gray, 45°, 35% opacity, centered overlay. The stamp PDF itself is tiny — 1,142 bytes — because it holds one line of standard-font text. qpdf applies it to all three pages with repeat tiling, and the result is a valid 3-page, 3,096-byte PDF: bigger than the original, since each page now carries the drawing operators, but still email-small. Run the same job as an underlay on pages 1–2 only and you get a 2,887-byte file whose page 3 is untouched — page-level selection genuinely skips work, it doesn't blank-and-redraw.
Open the PDF in a watermark tool, type the stamp text (CONFIDENTIAL, DRAFT, COPY), set size, opacity, and rotation, choose which pages to stamp, and download the result. This tool draws the stamp with pdf-lib and applies it with a qpdf WebAssembly engine inside your browser — the file is never uploaded to a server, so it also works for confidential documents.
An overlay is drawn on top of the page content, so it always stays visible — the right choice when the stamp must be seen, and the only choice that works on scanned pages, which are full-page images that would hide an underlay completely. An underlay is drawn behind the content, so text stays fully readable and the watermark only shows in the margins and white space. Use underlay for letters and reports you want to keep readable; overlay for drafts, copies, and anything that must be unmistakably marked.
For a diagonal one-word stamp on US Letter, 40 to 60 pt with 25 to 40 percent opacity is the readable-but-not-bludgeoning zone: at 48 pt, the word CONFIDENTIAL measures 357 pt wide, about 58 percent of the page width, and 35 percent opacity keeps body text legible underneath. Go bigger and bolder (60 pt, 50 percent) for draft copies nobody should mistake for final; lighter (28 to 36 pt, 20 to 25 percent) for tiled patterns so the page stays usable.
No, and any tool that implies otherwise is overselling. A watermark is regular page content — determined users can crop, cover, or edit it out in any PDF editor. What it does is mark provenance visibly and create a clear record of ownership, which matters for drafts, deposition exhibits, and leaked-document tracing. If you need enforcement rather than deterrence, combine the watermark with encryption and usage restrictions.
Yes, with one rule: use overlay mode. A scan is a full-page image, so an underlay watermark drawn behind it is completely hidden. An overlay stamp sits on top of the image and shows normally, at any opacity you like.
No. The stamp is generated with pdf-lib and applied by qpdf compiled to WebAssembly, both running inside the page. After the engines load you can even go offline and keep watermarking; nothing is sent to, or stored on, any server.