Document Hack (A Technical Writer's Journal): The Acrobat and the Illustrator
http://www.poewar.com/index.php?p=48

Hewitt, John
Writer's Resource Center
2004

Abstract:

Using Acrobat, you can make minor edits to a PDF file, but Acrobat documents are very sensitive. Typing a single character can throw several lines off, destroy tables and cause all sort of other troubles. Alternately, it can be relatively uneventful and painless. You will not know until you type in that character.