How to Add a Watermark to a PDF Online — Free Text Overlay
Adding a watermark to a PDF stamps a text label — such as "CONFIDENTIAL", "DRAFT", "DO NOT COPY", or your company name — diagonally across every page as a semi-transparent overlay. Watermarks visually communicate the document's status, discourage unauthorised reproduction, and brand documents for distribution. They are standard practice in legal, financial, and corporate document workflows.
How the watermark is applied
PDF-lib adds the watermark as a text annotation layer directly into the PDF's page stream. The text is rendered in large, semi-transparent Helvetica at a 45-degree diagonal, centred on each page. Because it is embedded in the file structure (not just an overlay), the watermark appears consistently in all PDF viewers and cannot be hidden by adjusting screen settings.
Customisation options
You can set the watermark text, font size, opacity, colour (grey, red, or black), and the rotation angle. A grey, semi-transparent diagonal text at around 45° is the standard professional appearance — visible enough to communicate the status but not so heavy that it obscures the document content. Red watermarks are used for urgent statuses like "REJECTED" or "VOID".
Common watermark text and use cases
CONFIDENTIAL — for sensitive business, legal, or HR documents shared externally. DRAFT — for documents in review that should not be treated as final. FOR REVIEW ONLY — for documents sent to clients for feedback before approval. SAMPLE — for proposals, templates, or examples sent as demonstrations. Company name watermarks are used on branded documents to prevent content being repurposed without attribution.
Watermarks vs. password protection
Watermarks are a visual deterrent — they communicate status and discourage misuse but do not technically prevent copying or printing. For genuine access control, combine watermarking with password encryption. A document that is both password-protected and watermarked is both technically secured and visually marked.
Related PDF tools
After watermarking, you may want to add page numbers or compress the file before distributing. To combine this PDF with others, use the PDF merger.