Watermark PDF
Stamp CONFIDENTIAL, DRAFT or any text across your PDF's pages — position, opacity, size, color and page range, rebuilt live. Your file never leaves your device.
Live preview & download
The preview shows page 1 schematically; the real stamp uses the same placement math on every selected page. Nothing is zipped, nothing is uploaded.
Your PDF never leaves your browser. The text is drawn onto the pages in memory on your own device — no server call and no upload. Disconnect from the internet after the page loads and it still works.
Stamp a watermark on a PDF without uploading it
The usual way to mark a contract DRAFT or a report CONFIDENTIAL is to feed it to a watermark site that uploads your document to its server, stamps it there, and often gates the download behind a sign-up. For exactly the kind of file people watermark — unreleased contracts, board decks, manuscripts — that is backwards. This tool does the same job with zero upload: the stamping runs in your browser through pdf-lib, a pinned MIT library served from this page. Your file is read locally, the text is drawn onto each page in memory, and the stamped PDF is handed straight back as a download.
Three positions, computed per page
Pick one of three presets. Diagonal across center rotates the text 45° through the middle of the page — the classic stamp, hard to crop out and instantly readable. Horizontal across center is quieter and suits status labels like FOR REVIEW ONLY. Bottom-right corner keeps the mark small, inset 24 points from the edges — right for an attribution or a version tag. Placement is calculated from each page's own dimensions: a worked example — on an A4 portrait page (595.28 × 841.89 pt), a 48 pt diagonal stamp 300 pt wide starts at (203.5, 303.0) so its glyphs straddle the exact center; on a landscape page in the same document the math re-runs with the sides swapped, so mixed-orientation files come out right.
Only the pages you choose
Leave the page field empty (or type all) to stamp everything, or use the same range syntax as the Split PDF tool — literally the same parser, shared between the two pages, so the rules never drift: 2-3 on a 5-page file stamps only pages 2 and 3, 1-3, 7 stamps four pages, and end always means the last page. Bad input is refused with a specific error — 12 on a 10-page file is out of range, 5-2 is reversed — never silently "fixed" into stamping the wrong pages.
Honest limits: Latin text only, and not tamper-proof
Two things this v1 deliberately does not claim. First, the built-in Helvetica font encodes only WinAnsi (Latin) characters — accents like é, symbols like € and em-dashes work, but 日本語, Cyrillic or emoji would render as tofu boxes, so the tool detects them as you type and warns you, naming the characters, instead of producing a broken file. Embedding a full Unicode font would add megabytes to a page that currently loads in well under a second. Second, an overlay watermark is a label, not a lock: it is drawn as a text object on top of the page, visible on every copy and print, but someone with a PDF editor can delete it. That is true of every overlay watermark, including the paid ones. If you need an irremovable mark, flatten the pages to images first — PDF to JPG, then back to PDF — accepting that the text stops being selectable.
What stays untouched
Your pages are not re-encoded: text stays selectable and searchable, vector graphics stay sharp, images keep their original bytes. The stamp adds one small text object per selected page plus a single embedded standard font — typically a few kilobytes. Everything rebuilds live on every change: drag the opacity slider from 0.3 to 0.15 and the preview and the downloadable file both update; there is no Apply button to hunt for. A subtle stamp reads best at 0.1–0.2 opacity over text-heavy pages; 0.3 (the default) suits scanned pages where the mark competes with photos.