How to Actually Redact a PDF (Not Just Draw a Black Box Over It)
A surprising number of real-world data leaks happened because someone "redacted" a document by drawing a black box over text in an image editor or a PDF annotation layer — the box sits on top of the text, but the text itself is still there underneath, selectable, copyable, and recoverable by anyone who knows to try. Proper redaction has to remove the underlying data, not just hide it visually.
Why a black box isn't redaction
PDFs store text as actual text data, separate from how it's visually rendered. A rectangle drawn on top, even one that looks solid black, is a separate layer sitting above the text — the text layer underneath is untouched. Anyone can select the "hidden" text and copy it out, or in some cases even see it directly by opening the file in a different viewer that doesn't render the annotation the same way. This exact mistake has exposed social security numbers, financial details, and confidential case information in real published documents.
What real redaction does instead
Redact PDF permanently removes the selected text and any images in the marked area from the document's underlying data, then replaces it with a solid black region — so there's nothing left to select, copy, or extract, because the information is actually gone, not just covered.
How to use it correctly
- Select the exact text or region that needs to be removed — names, account numbers, addresses, anything sensitive.
- Double-check for the same sensitive information appearing more than once in the document (a header, a footer, a repeated table row) — each instance needs its own redaction mark.
- Export the redacted version as a new file, and don't share the original alongside it.
Double-checking your work
Before sending a redacted document out, it's worth confirming the sensitive text is genuinely gone rather than trusting the process blindly. Compare PDF can highlight every difference between the original and the redacted version, which is a fast way to visually confirm exactly what changed and that nothing sensitive was missed.