Add Watermark to PDF
Choose a PDF, then adjust the watermark text, size, opacity, and angle — the download updates automatically. Nothing you upload ever leaves your browser.
How this works without a server
Once you choose a PDF, its original bytes are kept untouched in
memory. Every time you adjust a setting, this tool loads a fresh
copy of the document from those original bytes with pdf-lib — never from a previously-watermarked
version — so changing the opacity or rotation ten times never
stacks ten overlapping watermarks. On that fresh copy, it embeds
a standard Helvetica font, measures your watermark text at the
chosen size, and draws it as real vector text centered on every
page, rotated to your chosen angle and set to your chosen
opacity, using pdf-lib's built-in rotate and opacity options. The result is packaged into a
downloadable file with Blob and a browser download
link — no page is ever rasterized, and no file ever touches a
network.
Worked example
Leave the defaults — text "CONFIDENTIAL", size 48pt, opacity 0.3, rotation 45° — and upload a standard US Letter page (612 × 792 points). pdf-lib measures "CONFIDENTIAL" at 48pt Helvetica, centers it at roughly x = 306 minus half that width and y = 396 (the page's exact center in both directions), then rotates it 45° counter-clockwise around that point at 30% opacity. The result is a large, legible-but-unobtrusive diagonal watermark running corner to corner, identical on every page of the document.
Frequently asked questions
Is my PDF uploaded anywhere?
No. The file is read locally with the browser's File API, and pdf-lib runs entirely in your browser tab to draw the watermark and rebuild the file. Nothing is sent to a server, so confidential drafts and contracts never leave your device.
Why isn't there a live preview when I change the settings?
This tool is built purely with pdf-lib, which can write PDF pages but can't render them to an image the way a preview would need — that rendering is a separate library this tool doesn't load, to keep it small. Instead, every change to the text, size, opacity, or angle instantly regenerates the download link, so you can re-download and check it in any PDF viewer in a couple of clicks.
Does the watermark appear on every page?
Yes — the same text, size, opacity, and rotation is stamped once on every page of the document, positioned centered on each page regardless of that page's own size.
Can the watermark be removed later, like a layer in an image editor?
No, and that's by design — pdf-lib draws the watermark as real vector text merged permanently into each page's own content, not as a separate, removable layer. That permanence is what makes it a meaningful watermark rather than a suggestion; keep your original, unwatermarked file if you'll need it again.