Notation will not open a MIDI file as sheet music. How do I associate MIDI files?
To set the file association in most Windows versions you'll want to:
1. Use Windows Explorer to find one of your .not song files.
2. Right-click and then choose ""Open"" (or double-click).
3. Make sure "Always use. . ." is selected, and click "More apps".
4. Scroll down and click on "Look for another app on this PC."
5. Use the Search field to search the C: drive for "composer.exe" (for Notation Composer) or "musician.exe" (for Notation Musician). When you find the correct file, click on it in the Explorer dialog.
6. Click the "Open" button at the bottom of the dialog box.
Composer/Musician should then open that file, and then in the future you'll only need to double-click the .not file you want and Composer will automatically open it.