For PlayStation 4 (PS4), games and homebrew software are typically distributed in the .pkg (Package) file format. While "ROMs" is a term more commonly used for older cartridge-based consoles, the PS4 community uses .pkg files for backup and installation purposes. Essential Articles & Guides
How to check: Go to Settings > System > System Information. If your version is 9.00 or lower, you are eligible. If it is higher, you must wait for a new exploit (which may never come) or stay disconnected from the internet to avoid auto-updates. ps4 pkg roms
Encryption: Retail PKG files are protected by Sony's PFS (PlayStation File System) encryption. On a standard console, these can only be decrypted and installed if the user holds a valid license (RIF/RAP files) from the PlayStation Store. 2. Retail PKGs vs. FPKGs For PlayStation 4 (PS4) , games and homebrew
The PS4 emulation scene is in its infancy. While emulators like Spine and RPCS4 (in early stages) exist, they cannot run the vast majority of commercial PS4 PKG ROMs at a playable speed. If your version is 9