Recently, a report issued by the Italian defense department tried to use Adobe Acrobat to "redact" the text that was deemed classified by simply changing the color to be the same as the document background. In "Acrobat user gaffe exposes classified Defense information," posted by Government Computer news, an Italian Blogger discovered the problem shortly after the article was posted. Lesson for courts; make sure that sensitive information is completely eliminated from the document before creating the PDF. This may also require saving the document as text first.
