How to Add a Watermark to a PDF (Free, on Windows)

Adding a watermark to a PDF marks a document as a draft, a copy, or confidential without touching what it says. It is a five-second job locally, and the irony of most free web watermarkers is that they add their own watermark alongside yours unless you pay.

The short answer

1. Open PDF Tools from the BizTray tray.
2. Add the PDF — or a whole folder of them.
3. Set the watermark text, position, angle and opacity.
4. Apply to every page or a range, then save.

Nothing is uploaded, and BizTray never adds a mark of its own.

Getting it right, visually

A watermark that ruins legibility is worse than no watermark, because people recreate the document to get rid of it. What works:

• Opacity between 10% and 25%. Enough to be unmistakable, light enough to read through. Above about 30% you are fighting the body text.
• Diagonal, roughly 45°. It crosses the text grid instead of running along it, which reads as a mark rather than as content — and is harder to crop off.
• Behind the content where possible. The text stays crisp and the watermark still covers the page.
• Short. DRAFT, CONFIDENTIAL, COPY, NOT FOR DISTRIBUTION. A sentence set diagonally across a page is unreadable in both directions.
• Grey rather than colour, unless the colour means something. Grey survives black-and-white printing and photocopying legibly.

What a watermark actually achieves

Be realistic, because this gets oversold:

• It does deter. A page stamped CONFIDENTIAL diagonally is visibly not meant to circulate, and that alone changes behaviour.
• It does provide context that survives. Six months later, a page stamped DRAFT is still obviously a draft — which is exactly when that matters, long after the covering email is forgotten.
• It can make copies traceable. Watermarking each recipient's copy with their name means a leaked page identifies its source. This is the single most effective use of the feature.
• It does not prevent anything. Copying, printing and editing all still work. If you need the contents restricted, add a password.
• It is not permanent. A watermark on its own layer can often be stripped by determined software. Flattening afterwards makes that considerably harder — worth doing whenever the watermark carries weight.

The honest summary: a watermark is a sign, not a lock.

The batch case

The genuinely tedious version of this job is watermarking every document in a folder — a set of drafts before circulation, or per-recipient copies of the same document. Doing that one file at a time through a web tool that caps you at three an hour is where the afternoon goes.

Locally there is no cap, so pointing the tool at the folder and running once is the whole task. If it is a recurring job — everything dropped into a "drafts" folder should be stamped — a Watch Folders rule can apply the watermark on arrival.

Doing it on your own machine

PDF Tools watermarks alongside page numbers, flattening, metadata cleaning and adding or removing passwords, with no page cap and no file-size ceiling. Documents you are marking CONFIDENTIAL are a poor fit for uploading to a stranger's server on the way to being marked confidential, which is the small absurdity local processing avoids.

Two practical notes:

• Watermark last. If you are also merging or reordering, do that first — then watermark the finished document so the mark lands consistently on every page.
• Check one page at 100% zoom before running a batch. Opacity that looks right at fit-to-window is often too heavy up close.

A note on why this is free

BizTray has no subscription, quota or forced watermark because it shares a portion of your spare internet bandwidth through a vetted partner instead of charging you. It relays other parties' traffic and never touches your documents. Sharing is switchable off from Settings or the tray, and the tools do not run while it is off. See How it's funded.

Related

• How to add page numbers to a PDF — the other finishing pass.
• How to flatten a PDF — making the watermark harder to strip.
• How to remove metadata from a PDF — cleaning what the file says about itself.