Open it with any text editor or re-import into MMANA-GAL for visualization.
Hobbyists often reverse-engineer commercial antennas and share the .maa simulation files. These are invaluable for analyzing performance before buying. mmana-gal antenna files
This is perhaps the most powerful use of these files. A "perfect" antenna in free space will behave differently when placed 30 feet above average ground. By loading an MMANA-GAL antenna file, you can change the ground parameters (conductivity and dielectric constant) to match your specific QTH (station location). Open it with any text editor or re-import