Andreas,
There's not really anything you can do with the cda files from a CD. They can't be converted to MIDI and they are not the files containing the music so they can't be converted to wav files which in any case are typically 30MB or more. (For that you need a "ripper" program.) The best you can do if you have the ear for it is to get the tune onto paper in staff notation or ABC format & take it from there.

Cheers,
Alan