Press the Music Button to access the Music Player controller to control playback and link a song in your iTunes library to a PDF file.
The Music Controller will control the playback of any songs linked to the current PDF. The -4 and +4 buttons will allow you to skip forward and backwards by 4 seconds. The slider will allow you to jump to any point of the song. The Start offset will allow you to start from a predetermined point from the beginning in seconds.