When you issue updated manuals as PDFs, users who are already familiar with the software/device will not read the entire manual just to find out what is new and what has changed. Creating a separate Release Notes document is not always an option. You can help them identify the new information or changes by indicating new/updated features using bookmarks, grouped under an appropriate heading (such as New/Updated:), pointing to specific locations in your PDF -- where Acrobat notes provide more information if necessary.
This is easy to achieve with the Extract quick-access bookmarks function (Bmk Extraction tab). In the source FrameMaker files, you insert hypertext markers in the sections which include new or changed items. When the documents are converted to PDF, these markers result in bookmarks, sorted under a user-defined heading. The bookmark text can include a short prefix (such as new: or changed: -- resulting in separately-sorted groups).
In the cases where you would like to provide more information, a note can be defined as part of the hypertext marker (for a longer note you can reference an external text file from within the marker). You can control the note's icon, color, location and initial open/close state; bookmark properties can include color and font style.