Two PDFs look identical: black rectangles over names and figures. One is genuinely redacted; the other has the names sitting underneath, copy-pastable by anyone. The difference is invisible on screen but structurally enormous.
Covered: rectangle on top
A black rectangle drawn as an annotation lives on a layer above the page content. The underlying text and images stay in the file, untouched. Open the file in an editor and you can remove the rectangle. Open it in a script and you can extract the text directly. This is what most casual redacting produces — visually correct, structurally a disaster. Don't ship sensitive documents this way.
Redacted: content removed
True redaction deletes the underlying content from the page's content stream and replaces the area with a solid block (or any pattern). After saving, there's no underlying text to recover. The page object no longer contains those words. Redact PDF does this properly: select the regions, save, and the data is genuinely gone. Always work on a copy so the original stays accessible if you need it.
Don't forget the side doors
Page content isn't the only place sensitive data lives. Metadata can carry author names, software details, original filenames. Attachments can carry whole other files. Annotations can have comment text. Form data can hold past submissions. A truly redacted PDF needs all of these cleaned. A final pass through Flint strips most. For high-stakes redaction, verify with a second tool before publishing.
FAQ
How do I check if my PDF is truly redacted?
Open in another viewer and try to select the redacted region with copy-paste. If you can copy hidden text, it isn't truly redacted. Modern viewers also show 'invisible text' on toggle.
Is text inside images redactable?
Page-level redaction doesn't touch image content. If a name appears in a photo, redact the image region itself, not the text layer. Run OCR first if you're not sure what counts as text.
Should I flatten after redacting?
Yes — flattening locks the redaction into the page so no annotation layer remains. Belt and braces; prevents accidental future edits.
Cover and redact aren't the same. Use Flint's redact tool and the sensitive data genuinely leaves the building.