As CBY_TLSE said, there is a major difference between an audio file and a MIDI file. They are not interchangable.
However, there are audio to MIDI converters that can create MIDI files from audio files. But, like any language translation software, the results are rarely perfect.
If you are converting an audio file consisting of a solo instrument, you may get good results. Trying to convert an ensemble (multiple instrument) performance is likely to create a very disappointing result. However, even if imperfect, it may give you a good starting point and the MIDI file could be edited.
Here is one such conversion software, and they do offer a free trial...