PKG files are Mac OS X installation (setup) packages that contain installer scripts ('Scripts' file) and compressed installation files ('Payload' file) that are used to install Mac software applications onto a user's hard drive. With AnyToISO it's possible to extract PKG file contents and even convert it to ISO format, on both Windows and Mac OS X.
The following files have also the same format and are supported by AnyToISO: .mpkg, .pfpkg
Extract PKG on Windows
Extract PKG on Mac