Revisions viewed in Page Display Mode will not display an indication that a comment is required, allowed, or entered. However, when saving a document that requires comments, a dialog box displaying the text Please enter a comment for [Document Name] is opened:
Enter the necessary text and click OK.
To view the comment bubble icons, switch to Document Display Mode.
Depending on your configuration, if a document that allows revisions is split in the Separation Workspace, you may be prompted to add a comment for the original document and/or the newly created document.