MobileSheets will let you annotate the score. With the score open, tap the middle of the screen. This opens a menu at the top. Click the brush. This opens another menu. If you have a tablet pen, click the pencil and write all your notes onto your score. Click save, job done.because i dont read music i have to print the PDFs and write the notes on.. Then scan back onto my laptop and put on mobile sheets.
Or click the big A and type the notes onto your score. Again, click save, job done.