Guides · PDF redaction

The black box mistake: why covering text in a PDF doesn’t remove it

Gonzalo Sabater, lawyer · 28 October 2026 · 5 minutes

It is one of the most common mistakes when sharing documents: you open the PDF, draw a black box over a name or an ID number and send it. On screen the data is gone. But often it is still inside the file, and anyone can recover it in seconds.

Why it happens

A PDF is not a picture of a page: it stores text as text, with its position. A rectangle drawn with an annotation or shape tool adds a new layer on top. The original text stays underneath, untouched.

The same happens when you highlight text in black in Word and export to PDF, or set black text on a black background.

How to check in ten seconds

1. Open the redacted PDF.
2. Select the covered area with the cursor (or press ⌘A / Ctrl+A to select everything).
3. Copy and paste into a blank document.

If the name or number you thought was hidden appears, the redaction failed. You can also search (⌘F): if it finds the value, it is still there.

Other places where data hides

• Metadata: author, company, document title.
• Comments and annotations that don’t show when printed.
• Form fields with their saved values.
• Images (a scanned ID, a signature, a stamp) with no selectable text that can still be read.
• In Word: headers and footers, notes, tracked changes and hidden text.

How to redact a PDF properly

Redaction has to remove the content, not cover it. Professional redaction tools (and Maskwise) do this: they strip the text and images underneath and save a new page where the data no longer exists.

Then check the result: repeat the copy-and-paste test, or let the tool do it. Maskwise reads every redacted PDF again, with text recognition on the pages that need it, and if it cannot check something it says so with a “NOT VERIFIED” notice.