[Zubersoft]

I'm really sorry you ran into an issue with your file being corrupted or damaged! If you go to Settings->Storage and note the storage location, then look for the PDF used by the song under the storage location, what size is it? If you try to load it in another application, does it load? Or is the file damaged? If the file is damaged, then there may not be a way to recover it, unless you can happen to run it through a PDF repair program that can fix the errors in it. 

There is no backup that MobileSheets creates, so if you haven't created a library backup file recently under Settings->Backup and Restore->Backup Library, and there is no way to repair the PDF, then you would need to recreate the annotations. 

Mike