Add a watermark to a PDF

Choosing a PDF watermark that works

• Say why. DRAFT, CONFIDENTIAL, SAMPLE or a client's name tells the reader how to treat the document.
• Name the reader for leaks that matter. A watermark such as "Prepared for Priya Shah, 18 Oct" makes a forwarded copy traceable to the person it was sent to.
• Keep it readable underneath. An opacity of 20 to 35 percent keeps the text behind it legible.
• Repeat it if it must survive cropping. A single stamp in the middle is easy to cut out of a screenshot; a repeated pattern is not.

DRAFT, SAMPLE and CONFIDENTIAL: which preset when

The four presets above the text box set the wording, colour, opacity, angle and placement in one click. Change anything afterwards.

Preset	Use it for
DRAFT	A version that is not final: a policy under review, a proposal before sign-off, a handout still being checked. Grey, so the page stays easy to read.
SAMPLE	Example pages that must not be used as the real thing: a sample certificate, a worked exam answer, a template shown to a class. Repeated across the page.
CONFIDENTIAL	A document meant for named readers only, such as board papers or an HR letter. Red, in the middle of each page.
DO NOT COPY	Answer keys and assessment papers handed out for review. Repeated and light, so it shows on any photocopy.

What a watermark can and cannot do

The watermark is added as text on top of each page, using the open-source pdf-lib library. It shows in every PDF reader and when printed. It discourages copying and makes a leaked copy easy to recognise, but it is not a lock: someone with PDF editing software can remove it, and the document can still be read and copied. To stop people who should not see the document, add a password with the PDF password tool, and add the watermark first, since an encrypted PDF cannot be watermarked.

Other ways to watermark a PDF

In Microsoft Word, add the watermark under Design, then Watermark, before you save as PDF. In Adobe Acrobat (the paid version), use Edit PDF, then Watermark, then Add. On a Mac, Preview has no watermark feature, so use this page.

Know who read it

A watermark tells a reader the document is confidential. It does not tell you whether they read it. Share the watermarked PDF as a FileSeen link and you get an email when it is opened, the total reading time, who opened it and how long they spent on each page.