About attachments
With the command you can attach files to the current PDF document so they function
as comments. Attach a wide range of text or picture files at a given location in
the document.
Use the Attachments Panel to attach files that do not appear as comments.
With the command you can record or attach WAV sound files as comments.
You can use the Attachments panel to attach any file that is not a comment. In this case a wide range of file types is supported, including mp3.
Files or Sounds attached as comments can be removed with the Flatten Document command. In this case attachments added through the Attachments Panel are not removed, because they are not comments or annotations. All attachments (comments or not) can be removed with the Remove Document Elements command.