PDF Watermark

How PDF watermarking works

Watermarking adds semi-transparent text diagonally across every page of a PDF. The original content stays fully readable underneath while the watermark makes the document's status immediately clear.

This tool uses the pdf-lib library entirely in your browser. It loads your PDF, draws the watermark text at a 45-degree angle across each page, then saves a new PDF. Your file never touches a server.

When to watermark PDFs

PDF watermarking is essential whenever you need to communicate a document's status or protect its content without preventing anyone from reading it. Legal professionals regularly watermark draft contracts with "DRAFT — NOT FOR FILING" to prevent premature execution of agreements that are still under negotiation. A paralegal reviewing a 50-page merger agreement can watermark every page so that even if a single page is photocopied or screenshotted, its draft status remains evident. This simple layer of protection prevents embarrassing or legally problematic situations where an unapproved version circulates internally or externally.

Corporate teams handling confidential information use watermarks as a visual reminder of document sensitivity. An HR manager distributing employee compensation summaries might stamp each page with "CONFIDENTIAL" to reinforce that the information should not be discussed outside the management team. Financial analysts preparing quarterly earnings previews before public release use watermarks to ensure recipients understand the preliminary nature of the data. The watermark becomes a constant visual cue that persists across every page, making it far more effective than a single cover-sheet disclaimer that can be easily separated from the document.

Creative professionals and content creators use watermarks to protect their work when sharing samples or previews. A photographer sending a portfolio preview to a potential client can watermark each image with "SAMPLE — FOR REVIEW ONLY" to discourage unauthorised use. An author preparing an advance reader copy of their manuscript might stamp every page with "UNCORRECTED PROOF" so that reviewers and beta readers understand the content is still being edited. Freelance designers sharing mockups and concept boards use watermarks to prevent clients from using the low-resolution previews in place of a paid final delivery, protecting both their intellectual property and their livelihood.

Educational institutions and government agencies use watermarks to mark documents for specific purposes. A university registrar issuing unofficial transcripts might watermark them as "UNOFFICIAL — NOT A VALID CERTIFICATE" to prevent misuse of the document. Government agencies processing public records requests can apply watermarks indicating the date of release or the specific request number for tracking purposes. In each case, the watermark serves as both a security measure and an audit trail, embedding contextual information directly into the document that cannot be easily removed.

How to use the PDF watermark tool

Client-side processing with pdf-lib

This tool processes your PDF entirely in the browser using the pdf-lib JavaScript library. When you upload a file, it is read into memory on your device and never transmitted anywhere. The library loads the PDF structure, iterates through every page, and draws the watermark text at a 45-degree angle using the embedded Helvetica font. Each page is individually processed to ensure the watermark is positioned correctly regardless of page dimensions or orientation.

The watermark opacity is controlled through the RGBA colour model's alpha channel. A value of 0.3 (30% opacity) blends the watermark text with the underlying page content at a ratio where both remain visible. The tool multiplies your slider input by 0.01 to convert the percentage into the 0-to-1 range expected by the library. The colour picker value is converted from hexadecimal to RGB floats, then combined with the alpha value to produce the final watermark colour.

Font rendering uses the built-in Helvetica font that pdf-lib ships with, so no external font files need to be downloaded. The text is drawn at the specified font size using the drawText method with a rotation of 45 degrees applied via the degrees helper. Each page is saved with the watermark overlaid and the complete document is exported as a new PDF file. The original PDF remains completely untouched — a new file is always created containing the watermarked content.

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