Editing tips from the NSA
There are a number of pitfalls for people trying to amend a sensitive Word document for public release as a PDF. Here is the NSA's advice on typical traps.
Redaction of text and diagrams Covering text, charts, tables or diagrams with black rectangles, or highlighting text in black…is not effective, in general, for computer documents distributed across computer networks (i.e. in "softcopy" format). The most common mistake is covering text with black.
Redaction of images Covering up parts of an image with separate graphics such as black rectangles, or making images "unreadable" by reducing their size, has also been used for redaction of hardcopy printed materials. It is generally not effective for computer documents distributed in softcopy form.
Metadata and document properties In addition to the visible content of a document, most office tools, such as (Microsoft) Word, contain substantial hidden information about the document. This information is often as sensitive as the original document, and its presence in downgraded or sanitized documents has historically led to compromise.
Source: NSA Information Assurance Division report
Quoted from: Editing tips from the NSA | CNET News.com
