An Audio annotation is a short sound recording embedded in the file.
It appears as a loud
speaker icon on the document’s
page
.
To add an Audio record:
In the Annotation pane:
Select Audio note in the drop-down list of Annotation types
Click on the page where you want the icon of the audio note to be placed
Record your audio annotation by using the recording buttons
You
can move the position of your audio comment when it is selected and
the move cursor appears 
Edition options:
Icon color: quick color selection or advanced color selection

Record: Click Record for the system to start the recording. The label says 'Recording...' and you can see the time elapsing.
Stop: Click Stop to stop the recording or the playback.
Pause: Click Pause to suspend the recording or the playback. Click record, play or pause button to resume the action.
Play: Click Play to play the recording. The label says 'Playing...' and you can see the duration time of your recording elapsing.

Recording buttons only

Full interface for Audio annotation
Default features of an Audio record:
Recording buttons are enabled only when relevant.
A confirmation box is displayed before overwriting an existing record.

The internal microphone (built-in) of your Mac is used to register the audio notes. Please refer to the System preferences/Sound if you wish to change the device for sound input. The MAC help can provide you more information.

To play an Audio annotation in the PDF export (Acrobat Reader):
Click on the loud speaker icon
. The audio
record is played on the
default audio output of your device.
For more general information on annotation mode, see chapter Using_Annotations.