Just like any kinds of file formats that you may know of, the APK files are allowed to have any kind of name that is needed. The only thing that has to remain constant is the end which should be .apk. They are a kind of archive file and found in the zip format packages that are based on JAR format .apk is the filename extension. Installation One can install the files in the devices that are Android powered just the way we install software on the PC.
When one downloads and then installs an application on Android from official sites or other unofficial sites, they are actually installing APK ion the device. It is possible for a person to install APK files directly in devices. This can be done without necessarily downloading them from any network. You can use a desktop computer and use different communication programs.