Add a Text Watermark to a PDF

Features

• Chinese, Japanese and any other script (browser fonts, not the built-in PDF ones)
• Four layouts: tiled, centred, footer, and a custom position by percentage
• Angles of 0°, 30°, 45° or 90°
• Four opacity steps from 6% (very faint) to 50% (heavy)
• Colours: grey, black, red, blue
• Three sizes, scaled to the page width so different page sizes look consistent
• Watermark only certain pages (ranges such as 1-3,5)
• One render per distinct page size, so large documents stay fast
• The watermark is a layer: the original text is untouched and stays searchable

How to use

1. Drop a PDF in
2. Enter the watermark text and pick the layout, angle and opacity
3. To watermark only some pages, give a page range
4. Download the result

FAQ

Can the watermark be removed?

It can, though not easily — which is the point. The watermark is placed as an artwork layer on each page, so a PDF editor can select and delete it (a little easier than a watermark burned into the content stream), but that means going page by page. If you want it hard to remove, the tiled layout is far more annoying than one centred mark, since there are dozens to delete. Note also that the layer leaves the text untouched: searching and copying still work.

Why can the watermark not be "screen only"?

That is what optional content groups (OCGs) do — two versions of the content in one file, one shown on screen and one printed. pdf-lib cannot create OCGs, and it is the only PDF-writing library available in the browser. So this watermark appears both on screen and in print. For that effect you need desktop Acrobat or a professional layout tool.

What opacity should I use?

The default 12% is readable on screen without making the text underneath hard to read in print. Business documents sit at 6–12%; anything you want to stop people reusing (quotes, proofs) at 25%; 50% is close to covering the text and belongs on VOID stamps. Remember that on a black-and-white printer the watermark becomes a grey dot pattern — at 6% it may not print at all, so use 12% or more for anything meant to be printed.

Is the file uploaded?

No. The watermark is generated and written into the PDF in the browser, with no network requests at all, and it works offline. Contracts, quotes and internal documents are exactly what should not pass through someone else's server.