There is only one file type that uses the .MYR extension:
Myriad Music File
An MYR file is music file used by Myriad music applications such as Melody Assistant, Harmony Assistant, and Melody Player. It contains sheet music and instrumentation for a musical composition. MYR files can be played back in the software and exported to various audio formats, including .WAV, .MP3, and .MID.
Updated: April 25, 2017