[Zubersoft]

If you enable Settings->Import Settings->Automatically Add Matching Audio and then import PDFs you've already imported, MobileSheets will automatically add the audio files to the existing songs in your library. So just use Import->Batch Import if you have a large number of PDFs to process. You will need to have audio files that match the PDF filenames though, i.e. test.pdf and test.mp3. 

Mike