Guide

How to watermark a PDF

Put a DRAFT or CONFIDENTIAL stamp, a faint tiled mark, or your logo across a PDF, without flattening the page or wrecking the text underneath. Here is how to do it and keep the file editable.

Text or image, over or behind

A watermark is an honest overlay: a mark drawn on top of (or behind) the page, while the real content stays untouched underneath. That is different from the fake overlays some editors use to pretend to change text. With pdfblah you can add:

• A text mark like DRAFT, CONFIDENTIAL, or PAID, in any size, colour, and opacity.
• A tiled diagonal mark repeated across the whole page, the classic "do not copy" look.
• An image, such as your logo or a stamp, placed where you want and made semi-transparent.

Do it online

1. Open pdfblah.com and drop in your PDF.
2. Add a change → Watermark. Type your text, or choose an image.
3. Tune it. Pick the position (centre, footer, corner), turn on tile for a repeated diagonal mark, and set the opacity so it does not hide the content.
4. Stack more if you like. A watermark is just one change; you can also replace text, add page numbers, or password-protect in the same pass.
5. Download. Your fonts, spacing, and metadata are kept exactly as they were.

Three ways to do it

Same engine every way, so the result is identical. Pick whichever fits:

• Online at pdfblah.com — nothing to install, free while we're testing.
• On your machine, free and private (nothing is uploaded): pip install pdfblah, then pdfblah gui opens the same tool in your browser.
• Command line, for scripts and bulk jobs:

pip install pdfblah

# a faint tiled "DRAFT" across every page
pdfblah watermark in.pdf out.pdf --text DRAFT --tile --opacity 0.15 --rotation 45

# your logo, top-right, semi-transparent
pdfblah watermark in.pdf out.pdf --image logo.png --position top-right --opacity 0.4

# a big centred CONFIDENTIAL on page 1 only
pdfblah watermark in.pdf out.pdf --text CONFIDENTIAL --size 60 --pages 1

The app and CLI are open source (MIT). See the pdfblah project on GitHub.

Tips

• Keep the opacity low (0.1–0.2) for a tiled background mark so the text stays readable.
• Use --under to place the mark behind the page content instead of on top.
• A watermark does not lock the file; to stop copying or printing, add a password and permissions.