See this for some food for thought on some of the ways digital alteration can fail you: http://security.stackexchange.com/questions/126932/how-secur...
NSA published guidelines in 2005 for how to safely redact PDF (as well as word) documents. The corresponding physical redaction guidance begins by suggesting that the inspector physically remove the information to be redacted with an xacto knife. They redact and release thousands of documents, if nobody has reversed their redaction process yet then it's good enough.
Also note the answer that points out underhanded ways to leak data.
You then go ahead to recommend just the thing that gp was making fun of: printing and physically altering the document instead of using a software tool.
Basically violent agreement: )
May is a pretty clear clue that the security "advice" which follows is fud. Your house may flood even if it's on top of a high hill, buy my insurance product.