ISO file. "Highly compressed" versions are often hosted on community sites like Approm.cc or shared via MediaFire links in YouTube descriptions.
Highly Compressed: Files are often shrunk from several gigabytes down to a few hundred megabytes for easy downloading. ISO file
You cannot play the true Mortal Kombat 9 (with Kratos, Cyber Sub-Zero, and the full story mode) via PPSSPP. However, if you want a 3D Mortal Kombat experience with a huge roster, the closest legitimate ISO is Mortal Kombat: Unchained . ISO file