Guitar Pro supports exports to several multimedia formats, including MIDI instrumental music. The latest versions of the program are still capable of import previously used versions of project, so you should have no trouble converting grp to midi files even in the most recent edition of Guitar Pro.
Convert Guitar Pro project to MIDI-sequention sound.
We found one software available in the database for this conversion.
Microsoft Windows software - convert gtp to midi on Windows
Multi-track editor and music composer for guitars
Convert from gtp file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.