Online sources offering a “PS4 PKG” are almost always one of these:

If you see files labeled "Fight Night Champion PS4 PKG" online, they are almost always one of the following: PS3 PKG Files

Fight Night Champion was never officially released as a PS4 title. It launched in 2011 for PS3, Xbox 360, and iOS. The mention of a "PS4 PKG" refers to unofficial methods—typically PS3 emulation, debug conversions, or custom firmware (CFW) installers.