[Zubersoft]

Open the smart button window in the bottom right corner of the song overlay (the icon with a finger tapping a rectangle) and you can tap the X icon to delete the smart button. You can long press a smart button in the list to edit it. 

In the companion application, you can't make a connection between PDF and .musx. You could have a hyperlink in the PDF file that, when tapped, loads a .musx file based on a relative path. You would then just need to ensure the .musx file is in the same directory as the PDF.

Mike