Adobe ACROBAT READER 7.0 Manual page 116

About reviewing documents
When you receive an Adobe PDF document that includes comments, you can view these
comments, open attached files, and play sound clips in Adobe Reader. If the creator of the
PDF document enabled commenting, you can also create, edit, and respond to the
comments. (See About Adobe PDF documents with additional usage rights.)
Reviews are either email-based or browser-based:
If the initiator sent you the document as part of an email-based review, special instructions
and toolbar options appear when you open the email attachment. You can add comments
to the document and then use the Send Comments button on the Commenting toolbar.
If the initiator sent you the PDF document as part of a browser-based review, special
instructions and toolbar options appear when you open the email attachment. You can
review the PDF document in a web browser or offline.