How to blur or black out text in a PDF (so it's really gone)
Step by step: blur or black out text in a PDF so it can't be copied back out. Why boxes drawn in Word or a PDF viewer fail, and how to check your file.
Updated · 2 min read
Do it now: free, in your browser, nothing uploaded.
Open Blur PDFThe short answer
Open the PDF in a tool that removes the text under the blur or box, not one that only draws on top of it. Then check the result by trying to select and copy the hidden words. If you can copy them, they were never hidden.
With Blur PDF, that takes about a minute:
- Drop the PDF into the editor. Names, emails, phone, account and ID numbers are highlighted for you.
- Accept the highlights you want hidden, and drag boxes over anything else (signatures, stamps, photos).
- Choose Blur, Pixelate or Solid in the Redaction style panel.
- Export. Every page is rebuilt from pixels, and the output is read again to catch anything still legible.
Why a black box often isn't enough
A PDF can hold several layers: the text itself, images, annotations and drawn shapes. When you draw a black rectangle in Word, a PDF viewer's comment tools or many online editors, the rectangle is just another layer on top. The words underneath are still in the file.
That's why poorly redacted documents keep making the news. In 2019, lawyers for Paul Manafort filed a court document whose blacked-out passages could be read by simply copying and pasting the text.
Test any redacted PDF before sending it: select the area, copy, and paste into a text editor, or drop it into the PDF Redaction Checker, which finds text still hiding under boxes.
Blur or black out: which should you use?
| Style | Best for | Watch out for |
|---|---|---|
| Solid (black box) | Account numbers, IDs, short text, anything legal | Looks heavy on photos |
| Blur | Photos, signatures, faces, long paragraphs | Short text can sometimes be guessed back |
| Pixelate | Faces and backgrounds | Low strength leaves text readable |
Short, structured text such as a 10-digit number is the risky case for blur, because there are only so many possibilities to try. See Can blurred text be unblurred? for why.
What happens to the rest of the PDF
Rebuilding pages from pixels has trade-offs worth knowing:
- Gone: text under boxes, document metadata (author, software), comments, form fields and hidden layers.
- Changed: text in the exported PDF is no longer selectable or searchable, and the file may be larger.
- Unchanged: how each page looks, apart from what you covered.
Questions
Can I blur text in a PDF without Adobe Acrobat?
Yes. A browser tool like Blur PDF does it for free, without uploading the file.
How do I know the text is really removed?
Try to copy the hidden area and search the PDF for a hidden word. If nothing comes back, it's gone. Blur Document also re-reads the export and warns you about anything still legible.