What opacity should I use for a watermark?

A low opacity (10–20%) makes the watermark subtle and easy to read through. Higher opacity (40–60%) makes it more prominent and harder to ignore. The default of 25% works well for most documents.

What colours are available for the watermark?

You can choose Gray (subtle, professional), Red (high visibility), Black (strong contrast), or Blue (formal/corporate).

Does the watermark affect the readability of the document?

At the default 25% opacity, the watermark is visible but does not significantly obscure the underlying content. Lower opacity settings are less intrusive.

Will the watermark appear when the PDF is printed?

Yes. The watermark is embedded in the PDF page content and will appear when printed, just as it appears on screen.

Yes, completely free. No account, no sign-up, and all processing runs in your browser.

Watermark PDF Online

Add a visible text watermark to your PDF. Customise the watermark text, adjust opacity so it doesn't obscure content, change the size and colour, then download the watermarked PDF instantly. All processing runs in your browser.

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How it works

This tool uses pdf-lib, a pure JavaScript PDF library. It loads your PDF in memory, draws your watermark text diagonally across the centre of each page in Helvetica Bold at the opacity and size you choose (scaled down on any page where it would not fit), and downloads the result.

Processing runs in your browser

All processing happens inside your browser tab. pdf-lib applies the watermark entirely in memory; our servers are not involved at any point.

Related operations

For tagging each page with a numeric label, try PDF page numbers. To bundle watermarked files into one PDF, use merge PDF. For shrinking the marked output, see compress PDF.

Frequently asked questions

What opacity should I use for a watermark?: A low opacity (10–20%) makes the watermark subtle and easy to read through. Higher opacity (40–60%) makes it more prominent and harder to ignore. The default of 25% works well for most documents.
What colours are available for the watermark?: You can choose Gray (subtle, professional), Red (high visibility), Black (strong contrast), or Blue (formal/corporate).
Does the watermark affect the readability of the document?: At the default 25% opacity, the watermark is visible but does not significantly obscure the underlying content. Lower opacity settings are less intrusive.
Will the watermark appear when the PDF is printed?: Yes. The watermark is embedded in the PDF page content and will appear when printed, just as it appears on screen.
Is this tool free?: Yes, completely free. No account, no sign-up, and all processing runs in your browser.

Last reviewed September 30, 2026

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