capella-scan 8 can open PDF sheet music directly.
Please pay attention to the "PDF options" in the "Open image" dialog: Here you can select two different methods for handling "Bitmaps":
Depending on how your PDF file was created, one or the other option may be better for note recognition. The differences are sometimes huge!
There is no option which is always right. Please try both if you are not satisfied with the recognition.
One more hint: If page 1 of your PDF sheet music is a cover page without notes, simply skip it in the "Open Image" dialog.