How to Redact Sensitive Information in a PDF
Quick answer: True redaction removes the underlying text, not just paints over it. PDFslime doesn't include a redaction tool yet — use a dedicated redaction feature in your PDF editor, and always verify by trying to select or search the "redacted" text afterward.
A shockingly common mistake: someone draws a black rectangle over sensitive text in a PDF, shares the file, and the "hidden" text is still selectable and copyable underneath the box. Proper redaction actually deletes the underlying text and image data — it doesn't just cover it visually.
Why a Black Box Isn't Enough
A rectangle drawn on top of text in most editors is just another object on the page — the original text layer is untouched beneath it. Anyone can select all the text on the page, copy it, or extract it programmatically, and the "redacted" content comes right along with it. Several real-world leaks (legal filings, government documents) have happened exactly this way.
How to Redact Properly
- Use your editor's dedicated redaction tool if it has one — look for a feature explicitly called "Redact" (not just "draw a shape" or "highlight"), which removes the underlying text/image data, not just paints over it.
- Also check embedded metadata and comments — redacting visible text doesn't clear document properties, hidden layers, or reviewer comments that might reference the same information.
- Flatten the document after redacting if your tool offers it, so nothing can be un-hidden or toggled back on.
Always Verify
After redacting, before you share the file:
- Try to select the redacted area with your mouse — if any text highlights, it wasn't properly removed.
- Use Ctrl+F / Cmd+F to search for a word you redacted — it should return no results.
- Check that copy-pasting a page into a text editor doesn't reveal the hidden content.
Frequently Asked Questions
Not currently. Use a dedicated redaction feature in a full PDF editor, then verify the result before sharing.
No — in most editors this only adds a shape on top of the page. The original text is still there underneath and can usually be selected, copied, or extracted.
Scanned pages are images, so drawing over them does hide the visible content (there's no separate text layer to leak) — but only if you flatten the result so the shape can't be moved or deleted afterward. If the scan has already been through OCR, that added text layer would also need to be removed.