Adobe Acrobat 7 Professional - Manual (Page 251)

Using Commenting Tools
About adding comments
Selecting tools to add comments
Adding note comments
Indicating text edits
Highlighting, crossing out, and underlining text
Adding stamps
Marking up documents using drawing tools
Adding comments in a text box
Using the Callout tool
Using the Pencil tool
Using the Dimensioning tool
Adding attachments as comments
Spell-checking comments and forms
Setting Commenting preferences
Changing the appearance of comments