How to add a watermark to a PDF
Stamping "confidential" or "draft" across every page needs either the original document or a tool built for it. Here is how.
What a PDF watermark is for
A PDF watermark stamps repeated text, such as CONFIDENTIAL, DRAFT, or a recipient's name as a copy marker, across every page, usually as a diagonal, semi-transparent overlay that doesn't block reading the content underneath. It is meant to discourage a document from being redistributed as if it were final, or to trace which copy went to whom.
If you still have the original document
Word has a built-in watermark feature (Design, Watermark) that adds text before exporting to PDF, and it is the easiest path when the source file is still available. This does not help once the document only exists as a PDF, which is the more common situation.
On a Mac, Windows, iPhone or Android
None of the built-in PDF viewers on any platform, Preview included, can stamp a watermark across an existing PDF's pages; Preview's Markup tool can add text to one page at a time, but not automatically repeat it across every page of a multi-page document.
A tool that stamps every page at once
Stayput's watermark PDF tool stamps text across every page in one step, diagonally, repeated, or in a corner, directly in the browser, whether or not the original document still exists. It works on a PDF from any source, including a scan or one someone else sent you.
Questions
Can I watermark a PDF I no longer have the original document for?
Yes, a tool that stamps the watermark directly onto the existing PDF pages works regardless of what created the file or whether the source document still exists.
Does a watermark block someone from reading the document?
No, a proper watermark is semi-transparent and placed so it doesn't obscure the text; its purpose is visibility as a marker, not blocking access to the content.
Can I put a different watermark on each copy, like a recipient's name?
Yes, since the watermark text is set per file, each copy sent to a different person can carry that person's name or a unique copy number, useful for tracing which copy leaked if a document is redistributed.
Does watermarking a PDF change its other content?
No, it adds a new layer of text on top of each page without altering the existing text, images or layout underneath.