Redaction and document metadata leakage have been in the news lately based on various public incidents.
This is not proper redaction!.
Adobe has been made aware of customers posting public documents that have not been redacted properly to remove sensitive information. The most common user error is shown above. What appears to be an opaque rectangle over some text, is actually the same color font and background applied together. If you select the above text, copy it to the clipboard, and paste it into another application – you’ll see what was redacted!
For the proper way to redact documents in their source form and PDF, Adobe has written a whitepaper titled “Redaction of Confidential Information in a Document“.
The National Security Agency Information Assurance Directorate has also provided guidance in a document titled: “Redacting with Confidence: How to Safely Publish Sanitized Reports Converted from Word to PDF”