You can use the InfoSetter tool to set document information pertaining to your PDF document(s). This tool allows you to set or change the standard PDFs document information fields as follows: Title, Subject, Author, Keyword, Index, Base URL.
OK, so you want to stamp your document. Maybe you need to give reviewers some advice about the document's status or sensitivity. This tip from author Ted Padova demonstrates how to add stamps with the Stamp Tool along with related comments.