Files with the APK extension comprises of the application programs that have been generated for the Google’s Android mobile based operating system. This Android platform is based on the Linux Operating system and was primarily designed by the Open Handset Alliance for use on the Smartphones, nevertheless, the Android platform is now available on the tablets in addition to the mobile phone usage.
Such files that consist of the APK file format is useful in storing the files that are required to run one Android application on the similar mobile device. These APK extensions are compressed file archive that contains the codes for the program, mainly the application resource files and the AndroidManifest.xml
In addition to the problem described above, i.e. the lack of the appropriate application to support the .APK file, there may be several reasons that cause problems with opening and operation of the data format:
A quite common problem is the lack of application in the appropriate version. Even if you have an application, with the help of which you should open the .APK file, you may have a problem with it because of its version. Perhaps in previous versions the application has not yet supported the .APK file, so download the update and check again.
If you have already installed the appropriate application, and it is the correct version, the file may not open correctly, because the operating system does not have information that this program supports the file. So you need to "show" which program the computer should use. To do this:
It also happens that the file you want to open is corrupt and therefore there is no such possibility. In this situation, you should find its different version, or ask a person from whom you got, to send it again.
APK (Android Application Package) file format is a package distribution file format used by Android applications – basically it’s Android app installation file. APK file contains all required resources needed to install and run given application under Android OS environment, including program code, necessary data and assets, certificates and manifest file. APK files are usually downloaded to mobile devices directly from Google Play Store.
APK file structure and package creation
Android apps are created with Android Studio software. First, the application is compiled, and then the generated file is put into a container file. APK file is basically a compressed ZIP archive with .APK extension, and similar in structure to JAR file container.
Key files and folders in APK package
*Source: https://www.file-extension.info/format/apk