If you have access to view a document, you may attach comments to that document.
To attach Comments to a document:
  1. Select the document.
  2. Click on the Properties icon in the Action column.
  3. At the properties window, click on the Comments link.
  4. At the Comments window, click on the Add button.
  5. Add your comment.
  6. Click OK.
You may delete comments if you own the document or if you have attached the comment.

To delete a document comment:
  1. Select the document.
  2. Click on the Properties icon in the Action column.
  3. At the properties window, click on the Comments link.
  4. At the Comments window, click on the delete button next to the comment you wish to remove.
Version Comments:
Version comments are entered at the time of first publish and subsequent check ins. Only users with access to change the document can enter these comments. They are mainly used to create notes about the specific version, and not the document in general. To view Version Comments, perform the following:
  1. Select the document.
  2. Click on the Properties icon in the Action column.
  3. At the properties window, click on the Versions link.
  4. Version specific comments are displayed under each version.
You may also view version comments by clicking on the Comments link in the properties window. In this window, all comments are displayed.