Add Watermark to PDF

How to add a watermark

1. Add a PDF by clicking the dashed box or dragging the file onto it.
2. Type the watermark text. The default is CONFIDENTIAL.
3. Set the font size (10–200 points, default 50) and the opacity (0.05 is barely visible, 1 is solid; default 0.3).
4. Set the rotation in degrees. 0 is horizontal, the default 45 rises from lower left to upper right, and 90 reads from bottom to top – angles turn counter-clockwise.
5. Pick a color – gray, red, blue or black – and press Add Watermark.
6. Download watermarked.pdf. Your original file is not changed.

How the watermark is applied

The tool runs the open-source pdf-lib library in your browser. It loads your PDF, takes the standard Helvetica font and, on every page, draws your text once so that its middle sits at the centre of the page, with the size, angle, color and transparency you chose. The watermark is added as an extra layer of page content drawn on top of what is already there; the existing text, images and vector graphics are not touched or re-rendered, so text stays selectable. The new file is written in memory and offered as a download – nothing is uploaded.

Choosing a size

An A4 page is 595 points wide and a US Letter page 612. The word CONFIDENTIAL in Helvetica is about 7.3 times as wide as the font size, so at 50 points it is roughly 367 points long. At a 45° angle it spans nearly the full width of the page at around 100–110 points. A short word such as DRAFT (about 3.3 times the font size) still fits diagonally at the maximum of 200.

Tips for readable, useful watermarks

• Stay subtle: gray at an opacity of 0.2–0.3 labels the document without hiding the content. Use red for DRAFT or VOID when the label must not be missed.
• Personalize copies: a watermark such as "Copy for J. Smith – 27 Sep 2026" discourages forwarding and shows where a leaked copy came from.
• Label copies of ID documents with their purpose and date, for example "For rental application only – Sep 2026". Our guide on handling sensitive PDFs explains why.
• Watermark last: merge and split first, then add the watermark to the final document.
• Keep the clean original in case you need an unmarked copy later.

Typical uses

• Marking drafts that are still under review.
• Stamping CONFIDENTIAL or INTERNAL on documents shared outside a team.
• Labelling SAMPLE or PREVIEW on proofs, templates or design mock-ups.
• Tagging scanned ID or bank documents with the purpose they were shared for.

Limitations and alternatives

• It is a label, not protection. The watermark is ordinary page content, so someone with a PDF editor can select and delete it. To make removal much harder, convert the watermarked file with PDF to JPG and rebuild it with JPG to PDF – at the cost of selectable text and a larger file.
• One line of text per page, always centred and on every page: no images or logos, no tiling, no custom fonts, no page selection. To mark only some pages, split the document, watermark that part and merge the parts back in order.
• Characters: Helvetica covers English and Western European text only; Chinese, Cyrillic, Greek, emoji and similar characters cause an error.
• Unusual pages: pages stored with a rotation flag (common for scanned landscape pages) are stamped in their unrotated orientation, and pages whose visible area is cropped may show the watermark off-centre.
• Encrypted or signed PDFs: password-protected files cannot be opened, and adding a watermark invalidates a digital signature.
• Alternatives: Adobe Acrobat's watermark feature supports images, page ranges and tiling. The free command-line tool qpdf can stamp a page designed elsewhere onto every page: qpdf input.pdf --overlay stamp.pdf -- output.pdf.

Related tools

• Merge PDFCombine documents before stamping them.
• Split PDFSeparate the pages you want to mark.
• PDF to JPGFlatten a watermarked file into images.
• JPG to PDFRebuild the flattened images into a PDF.

Further reading: Handling sensitive PDFs: local processing vs uploading.