Two ways to make text 'disappear' in a PDF: redact, and draw a black box on top. They look identical onscreen. They behave very differently when someone tries to copy from the area.
This difference has cost lawyers their cases and journalists their sources. Here's how to know which one your tool is doing.
Black-out: just a rectangle
A black rectangle drawn over text is an annotation. It sits on top of the page content but doesn't change what's underneath. The text remains in the PDF's content streams. Any reader that respects content streams (Acrobat, Preview, browser readers) lets you select that text — the rectangle doesn't block selection, just rendering.
Redaction: strip and overlay
Real redaction removes the underlying text from the content stream entirely, then draws a black fill in its place. The text isn't behind the black; it's gone. Copy from the redacted area returns nothing. This is what Flint's redact tool does.
How to tell which you did
Save your file. Open it. Try to select text in the 'redacted' area. Two outcomes: (1) selection returns the original text — you black-boxed, not redacted. (2) selection returns nothing — you redacted properly. Always do this verification, especially for sensitive documents.
When black-out is acceptable
Cosmetic only — covering an old company logo on a presentation slide, hiding a minor visual element. Anywhere the underlying content isn't sensitive. For anything actually sensitive (PII, financial data, court filings), use real redaction in Flint or another tool with a dedicated redact function.
FAQ
Can I tell which one a tool does without testing?
Most legitimate redact tools have a 'redact' label and an 'apply' step that's clearly distinct from drawing. Drawing tools (highlighter, shapes) are not redaction.
What about PDF readers that 'remove redactions'?
Those tools remove the black overlay but the underlying text was already gone (real redaction). For black-box covers, removing the rectangle exposes the original text — that's the failure case.
Is there a one-click test?
Highlight the redacted area in the saved file. If you can select text, it's black-box. If selection is empty, real redaction.
What's the worst-case if I use black-out for sensitive content?
Anyone with a PDF reader can copy the 'hidden' text. Real-world incidents include leaked legal documents, journalist sources, and government reports.
Test your output. If it's not real, redact properly.