So as to come up with the APK file, one needs an Android program for Android to be compiled and then all parts packaged into a single file that contains the code of the program. This can be files like .dex files. The APK file also has to have the manifest, certificates, assets and resources files. 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.