Hy and thanks for you answer.
I tried the SmartScore Pro Demo and the PDFtoMusic Pro Demo:
1) SmartScore Pro works well allthough I'm working on scans of photocopies which aren't very clean.
2) PDFtoMusicPro works only with perfect PDF files. Very neat files which I converted from the tiff demos of SmartScore Pro don't work:
"The document cant be processed because it doesn't include any exploitable music data.
This PDF file has probably not been generated from a music notation software."
... but I would like to work on a scan from photocopies to make a piano reduction (for educational purposes).
So why does SmartScore Pro work and Lite doesn't?