The black-box mistake
Most PDF editors let you draw a black rectangle or highlight text in black. On screen, the information looks gone. It isn't. The rectangle is a separate layer on top of the page, and the original text is still in the file underneath. Anyone can select it, copy it and paste it into a text editor. Search engines can index it.
This has caught out law firms, government departments and companies, leading to published court filings and reports where the "redacted" passages were readable by copy and paste.
What real redaction does
True redaction removes the content, not just hides it:
- The text under the box is deleted from the page.
- Images under the box are cut or flattened.
- Nothing remains for copy, search or text extraction to find.
PDFWisely's Redact PDF does this by rebuilding each redacted page as a flat image with the marked areas blacked out. The original text on those pages no longer exists in the file. Pages you don't redact stay untouched and searchable.
Step by step
- Keep the original. Store an unredacted copy securely. Redaction is permanent.
- Search, don't scroll. Use Find to mark every instance of names, account numbers, addresses and reference numbers. Eyes miss things; search doesn't.
- Draw boxes for the rest. Signatures, photos, handwritten notes and anything in a scanned page.
- Check the easy-to-miss places. Headers and footers, tables, image captions, footnotes and appendices.
- Apply the redactions and download the new file.
- Remove hidden details with Remove PDF Metadata.
- Test it (see below).
The 30-second test
Open the redacted PDF and:
- Press Ctrl+A (or Cmd+A on a Mac) to select all text.
- Copy and paste it into Notepad, TextEdit or an email.
- Search the pasted text for the information you redacted.
If anything sensitive appears, the redaction failed. Don't send the file.
What to redact: a checklist
| Category | Examples |
|---|---|
| Identity | Names, dates of birth, signatures, photos |
| Contact | Home addresses, personal phone numbers, emails |
| Financial | Account and card numbers, sort codes, balances |
| Government IDs | National Insurance, Social Security, passport and driving licence numbers |
| Health | Diagnoses, prescriptions, medical record numbers |
| Third parties | Information about people who aren't part of the request |
In the UK, subject access requests under the UK GDPR often require redacting other people's personal data before disclosure. In the US, court rules typically require redacting all but the last four digits of Social Security and financial account numbers in public filings. Check the rules that apply to your situation.
Other hidden places information can hide
- Metadata: author names, company names, file paths. Remove it.
- Comments and tracked changes carried over from Word. Accept all changes and delete comments before exporting.
- Attachments embedded inside the PDF.
- Earlier versions: some PDFs save edits as additions, keeping old content in the file. Rebuilding pages, as true redaction does, removes these.
- Bookmarks whose titles contain names.
Redaction vs other tools
- White-out in Edit PDF covers content for presentation. It's not redaction.
- Flatten locks form answers and comments into the page. It's not redaction either.
- Protect PDF controls who can open a file. Use it alongside redaction when sharing sensitive documents, not instead of it.
Frequently asked questions
Is a black highlighter in my PDF app the same as redaction?
Usually not. Highlights, rectangles and comments sit on top of the page, and the text underneath can still be copied. Only a dedicated redaction feature, or rebuilding the page as an image, removes it.
Can redaction be undone?
Proper redaction can't be undone in the redacted file, which is the point. Always keep an unredacted original in a secure place.
Does redaction remove text from scanned pages?
A scan is already an image, so the box simply covers pixels. But many scans have a hidden OCR text layer, which must be removed too. Rebuilding the page as an image does this.
Do I need to remove metadata as well?
Yes. Metadata can reveal the author, organisation and editing history. Use Remove PDF Metadata after redacting.