How to Flatten Documents Securely
By Josh Simons on Jun 13, 2007
My Monday entry about the importance of flattening documents to avoid accidentally disclosing confidential or secret information was apparently too simplistic. As Kai points out, PDF documents are also prone to information leakage.
The example he cites involved a US government report on the accidental killing of an Italian agent in Iraq by American forces. A redacted version of the report was published online and then the "obscured" information in the document was subsequently exposed by an Italian blogger. I recommend visiting this site to see how easy it is to expose the supposedly "blacked out" information in that PDF report.
For those who need to be serious about redaction and related issues, the NSA has published a guide, Redacting with Confidence: How to Safely Publish Sanitized Reports Converted from Word to PDF.