Is white-out in a PDF safe? How to hide sensitive information properly
Last updated 2026-10-05
People black out an account number in a PDF by drawing a box over it and then share the file. The text underneath is often still there. Several well-known leaks have happened exactly this way.
Covering is not removing
A PDF is made of layers of instructions. Drawing a white or black rectangle adds one more instruction on top of the page; the original text instruction is still in the file. Anyone can open the file, select the area and copy the text, or use a PDF viewer's text extraction, and the hidden words appear.
How to test a file before you send it
Open the exported PDF in a viewer, press select-all, and paste into a plain text editor. If the sensitive text appears, it is still in the file. You can also search for a word you tried to hide: if the viewer finds it, it is there. Do this on the final file, not the version you were working on.
What the PDF Toolkit's Edit tab does
The Edit tab adds text, drawings, highlights, white-out boxes and images on top of the page. It leaves the original content untouched, which is what makes it good for filling forms and adding signatures, and it is also why its white-out is cosmetic, not secure redaction. We say so in the tool and in the terms for that reason.
Ways to remove information for real
The most reliable is to flatten the page into an image: print the redacted page to a new PDF, or take a screenshot of it and save that as a PDF, so the underlying text no longer exists. Another is to remove the whole page that contains the information. Use a dedicated redaction feature in your PDF software if you have one, and still run the select-all test afterwards.
Compress PDF also rebuilds each page as an image, which removes the text layer as a side effect, but treat that as a bonus and not a redaction method; check the result.
Do not forget the rest of the file
Sensitive details can sit outside the visible page: in the document properties such as author and title, in file names, in annotations and in earlier versions. For something genuinely confidential, create a new file from the flattened pages rather than editing the original.