As the home of Paramount Pictures, Paramount+ has Rango available to stream instantly. You can download the mobile app and save the movie offline to your device—essentially getting an official MP4 file, but wrapped in the app’s DRM (Digital Rights Management).
If you prefer to own a digital copy to store in your own cloud library (like Google Drive for personal use after purchase), you can find it on these platforms: Google Watch Action Data
Highlights include:
rango-google-drive-mp4