How to redact a PDF properly (and why black boxes fail)

Redacting is not the same as hiding

A PDF page is made of layers: the text you can select, pictures, drawings, and often extra information you never see, such as document properties, comments and earlier versions of the file. Drawing a black rectangle on top of a sentence adds one more layer. The sentence underneath is still there.

That is why court filings, government reports and business documents have leaked this way: someone covered the text, but the text could still be selected, copied or found with search. Real redaction deletes the content under the box, so there is nothing left to uncover.

Ways that don't work

• Black highlighter or a black shape drawn in a PDF editor: the text stays under it.
• Changing the text colour to black or white: the words are still in the file.
• Covering text in Word, then saving as PDF: depending on how it was done, the text can survive in the PDF.
• Taking a screenshot of the page: it can work, but you lose searchable text and quality, and it's easy to miss a page.
• Forgetting the hidden parts: a name you removed from the page can still be in the document's properties, bookmarks or comments.

How to redact a PDF in PDFZyro, step by step

1. 1Open the Redact tool and choose your PDF, or upload it.
2. 2Mark what to remove: select text, drag a box over an area (a signature, a photo or part of a scan), or use Search & redact to find every match of a pattern.
3. 3Search & redact can find Social Security numbers, email addresses, phone numbers, credit card numbers, dates, or your own words and phrases. Review the marks and remove any you want to keep.
4. 4Choose how the boxes look: black, white, grey or red, with optional text such as REDACTED.
5. 5Click Apply redactions. PDFZyro deletes the text, pictures and drawings under each box, and the redacted words are also removed from the document's properties, bookmarks and comments.
6. 6Keep Also remove hidden data ticked to clear metadata, attachments and earlier saves as well. The redacted copy is saved as a new version, so your original stays in your private history.
7. 7Download the redacted PDF and share it.

How to check that a redaction worked

Before you send a redacted document, spend one minute checking it, ideally in a different PDF reader:

• Search the document for a word you removed. It should not be found.
• Select the area around a redaction box, copy, and paste into a text editor. Nothing from under the box should appear.
• Open the document properties (title, author, subject, keywords) and check they don't contain removed information.
• Check every page, including headers, footers and attachments.

Redacting scanned documents

A scan is a picture of a page, so search can't find words in it until text recognition (OCR) has read them. Make the scan searchable with OCR first, then use Search & redact. You can also draw boxes over any area of a scan: the part of the picture under the box is blanked, not just covered.

A short redaction checklist

• Work on a copy, and keep the original somewhere safe and private.
• Search for every name, number and term that must go, not only the ones you can see.
• Remember headers, footers, tables, charts and pictures.
• Remove hidden data: metadata, comments, attachments and earlier saves.
• Check the result in a different reader before sharing.