Add a watermark to a PDF, free
Add a diagonal, semi-transparent text, like "CONFIDENTIAL" or "DRAFT", to every page of your PDF, right in your browser. No sign-up and your file is never uploaded to a server.
Keep editing this PDF?
Up to 100 MB per file · very long text on a narrow page can slightly overflow the edges
100% private — your file is processed on your device and never uploaded to any server.
How to add a watermark in 3 steps
Upload your PDF file
Drag or select the PDF you want to add a watermark to.
Type the text and pick the intensity
Type whatever text you want (for example CONFIDENTIAL) and choose Light or Bold.
Download your watermarked PDF
The text will appear diagonally, centered, on every page of the document.
Common use cases
Some of the most common ways to use this tool.
Mark a document "CONFIDENTIAL"
Make it clear that a report, contract, or proposal shouldn't be shared freely.
Mark a version "DRAFT"
Clearly distinguish a work-in-progress version from a document's final version.
Add your company's name
Mark quotes, dossiers, or materials before sending them to a client.
Mark a "COPY" of an original
Distinguish a copy of a certificate, diploma, or official document from its original.
Protect notes or teaching material
Add your name or your school's name before sharing notes or handouts with others.
Mark samples before sending them
Add "SAMPLE" to a catalog or portfolio before sharing it with a potential client.
Watermarking a PDF, explained
Adding a watermark with Unido means drawing the text you type, diagonally and semi-transparently, on top of each page's existing content, using Helvetica — one of the 14 standard fonts every PDF reader already has built in, with no font file to embed.
The transparency comes from a graphics state built into the PDF itself (an "ExtGState" with reduced fill opacity) that's switched on right before the text is drawn, and the diagonal tilt is set directly in the text matrix, with no need to recompute the position of anything else on the page. The font size is automatically fit to each page's dimensions, so the text stays centered and legible with nothing else to configure.
One honest limitation: because this tool uses a standard, non-embedded font, a very long watermark text on a narrow page can end up slightly overflowing the edges — for best results, use short phrases like "CONFIDENTIAL", "DRAFT", or your company's name.
Like every other Unido tool, the whole process happens in your own browser: the engine that parses the PDF and adds the text was written specifically for Unido, with no external libraries, and your file is never uploaded to any server.
Frequently asked questions
Is it free to add a watermark with Unido?
Yes, Unido is completely free, with no usage limits and no need to create an account.
Does my file get uploaded to a server?
No. The entire process happens inside your own browser. Your file never leaves your device or gets sent to any server.
Can I type any text I want?
Yes, you type whatever text you want — for example CONFIDENTIAL, DRAFT, COPY, or your company's name — and it's applied to every page of the document.
What happens if I type a very long text?
This tool uses a standard, non-embedded font and automatically fits the font size to the page's dimensions, but a very long text on a narrow page can end up slightly overflowing the edges. For best results, use short phrases.
Can the watermark be removed afterward?
The watermark is added as new content on top of each page, not as an easily identifiable separate layer, so a standard PDF doesn't offer a "remove" button without advanced editing tools. Always keep a copy of your original PDF without the watermark.
Does this replace the content of my pages?
No. The watermark is added as a new element on top of each page's existing content — nothing that was already there is ever deleted or replaced.
What's the maximum file size?
You can add a watermark to PDF files up to 100 MB.
Can I watermark a password-protected PDF?
No, this tool doesn't support encrypted or password-protected PDFs. Remove the protection from the file before adding a watermark to it.
Does it work on mobile?
Yes, Unido works in any modern browser, on both mobile and desktop, with nothing to install.
More tools
Merge PDF
Combine two or more PDF or Word files into a single document.
Merge my files Extract & splitSplit PDF
Extract specific pages or split a PDF into several independent files.
Split my PDF Convert formatConvert PDF to Word
Extract the text from your PDF and download it as an editable Word (.docx) document.
Convert to Word Convert formatConvert JPG to PDF
Combine one or more JPG images into a single PDF document.
Convert to PDF Convert formatConvert PDF to JPG
Turn every page of your PDF into a JPG image.
Convert to JPG Reduce sizeCompress PDF
Reduce the size of your PDF files by compressing the images they contain.
Compress my PDF Fix orientationRotate PDF
Turn every page of your PDF 90°, 180° or 270°, in seconds.
Rotate my PDF Number pagesAdd page numbers
Automatically add a page number to every page of your PDF.
Number my PDF