If you are using MIDI files for copyrighted music, with Notation or any other music software, and those MIDI files were obtained without permissions from or payment to the copyright owner, then this might
constitute a copyright violation. For this reason, we generally point Notation users only to non-copyrighted MIDI files.
If the MIDI file is for music that is in the public domain, and if the author of the MIDI file does
not require a copyright for his/her MIDI arrangement of the public domain music, then you do not need to purchase a copyright of the MIDI file or music. If the MIDI file is one that you have purchased, then the
party selling you the MIDI file is responsible for compensating any copyright owners of the MIDI file and/or music.
That said, a very large percentage of MIDI files that can be found on the Internet are for copyrighted music, for which the copyright owners are not being compensated. This is a gray area of copyright
enforcement that is even less settled than that for MP3 files. We (Notation Software) do not have legal experise in copyright issues and therefore cannot advise you about your obligations to music copyright owners for MIDI files that you convert to sheet music using Notation products.