How to Watermark a PDF for Free

Marking a document DRAFT, CONFIDENTIAL, or with your company name before sharing it is one of the fastest ways to prevent a document from being mistaken for something it isn't — a work-in-progress treated as final, or an internal document treated as approved for external use.

Watermark it in your browser (no upload, free)

The Watermark PDF tool on keptlocal stamps text diagonally across every page, entirely on your device.

1. Drop your PDF onto the tool.
2. Type the watermark text — up to 40 characters. "CONFIDENTIAL" is the default.
3. Pick a colour: gray, red, blue, or black.
4. Pick a size: small, medium, or large.
5. Adjust opacity with the slider — 10% (subtle) to 50% (bold).
6. Click Apply & download.

The text is drawn at a 45° angle across the center of every page, scaled proportionally to the page size so it looks consistent whether the document is A4, Letter, or a custom size.

When a watermark is (and isn't) the right tool

A visible text watermark is a communication device, not a security control — it makes a document's status obvious to anyone reading it, but it doesn't prevent someone from cropping, editing, or redistributing the file. Common, well-suited uses:

• Marking drafts so a work-in-progress document is never mistaken for the final version if it's shared before review is complete.
• Confidentiality notices on internal documents being shared with a limited audience — a visible reminder not to forward or publish.
• Sample or preview marking — publishers and stock content providers watermark previews so the full, clean version stays valuable.
• Attribution — stamping a company name or source across pages of a report being distributed publicly.

If you actually need to prevent unauthorized copying or opening, that's a different problem — see keptlocal's Protect PDF tool, which adds real AES-256 password encryption rather than a visible mark.

Choosing color and opacity

Gray at 20–25% opacity is the most common choice for a professional document — visible without competing with the body text for attention. Red at higher opacity (35%+) reads as more urgent, which suits "DRAFT" or "DO NOT DISTRIBUTE" marks where the goal is to be impossible to miss. Blue and black sit between the two, useful when a document's existing color scheme makes gray or red clash visually.

Privacy: what happens to your file

The watermark is applied entirely in your browser using pdf-lib, a JavaScript PDF library — your file is never uploaded. Open DevTools → Network while watermarking and you'll see no outbound requests. This matters for anything marked "CONFIDENTIAL" in particular: sending a confidential document to a third-party server just to add a confidentiality stamp is a bit self-defeating.

Watermark a PDF now with keptlocal's free Watermark PDF tool — no upload, no signup. Need real encryption instead? Try Protect PDF.