Grato Mário, this extension is required for the standard electronic reading system of this keyboard. That is, the pendrive it recognizes must contain .smf format files. I also know smf, which means Standard Midi Files. It would be a midi file pattern as I understand it from my internet search. But from the little contact I had with this keyboard, that's what I understood. It's to help a professional music friend who plays at night. What I got was the page https://www.converthelper.net/smf-to-midi. But the conversion fails. In other words it doesn't work. But for you to see that there is a possibility to convert from .mid to .smf or the other way around. I also found out that the Apple Program converts midi to smf, Logic X. See what can help me in the form of answers in this topic. But I need help inside Windows or Linux. Did I get to enlighten you?
Respectfully,
Miguel Archangel Ferreira Duarte Júnior.