I have a file that is used to store images, 3D models, sound files, and text- however I can not determine the filetype. WinRAR and 7Zip can not open the file successfully. The extension is .PKG however it is an archive (I am certain). Upon inspection with an editor, plaintext- suggesting nothing is encrypted- can be found and effectively changed in the application that loads the .PKG file. My goal is to extract images/sound from the file, so what steps do I need to take to figure out what type of archive this is?