This is one of the most consequential mistakes in document handling, and it happens constantly: someone draws a black rectangle over a social security number, a salary figure, or a confidential clause, exports the PDF, and shares it believing the information is gone. In many cases it isn't. The black box is just another visual object placed on top of the existing text, the text itself is often still there, underneath, fully intact and extractable.
Why a black box isn't redaction
A PDF page can have multiple layers of content stacked on top of each other. Adding a black rectangle with a basic annotation or drawing tool places a new shape object above the existing text, it doesn't touch or remove the text object underneath at all. Anyone who selects and copies the "hidden" area, or opens the file in a tool that lists all text objects on a page, can retrieve the original content the black box was meant to hide. This has caused real, well-documented data leaks in government and corporate documents where "redacted" filings were later found to contain fully recoverable sensitive text.
What proper redaction actually does
Real redaction, the kind performed by a purpose-built tool like PDF Redaction, identifies the specific text or image content in the selected area and deletes it from the document's underlying data, replacing it with a black mark that has nothing left behind it. After proper redaction, selecting the blacked-out area returns nothing, because there's genuinely nothing there anymore, not text hidden under a shape, but an actual gap in the content.
Checking your work before sharing
After redacting a document, it's worth verifying the result rather than trusting it blindly: try selecting text in the redacted area and confirm nothing copies out, and check the document's metadata separately, since author names, comments, and revision history can also leak sensitive information that a black box over the visible page never touches. Stripping that metadata with the PDF Metadata Remover is a necessary companion step to visual redaction, not an alternative to it, since the two protect against different kinds of leakage.