APK stands for Android Package (sometimes Android Package Kit or Android Application Package). This is the file format that Android uses to distribute and install applications. It contains all the elements that an application needs to be properly installed on your device. On the other hand, the application package files on iOS are called ipa files.
IPA stands for “iOS App Store Package” and includes a binary for the ARM architecture, which can only be installed on an iOS device. The Payload folder is the one that contains all the application data. It's impossible to install APK files on your iPhone, as these files are designed to run on Android devices. Android applications are compiled into the Dalvik executable file, which is present within an APK package. As for iOS, it executes files compiled from IPA, usually encoded with the Xcode language. The Android package with the apk file extension is the file format used by the Android operating system and several other Android-based operating systems for the distribution and installation of mobile applications, mobile games and middleware.
It's not possible to natively run an Android application on iOS (which works with iPhone, iPad, iPod, etc.). It's also impossible to convert an apk file to IPA for use on iOS, nor can you convert an APK to EXE to use the Android application on Windows. You can download ipa or apk files from any website, blog, etc. But Microsoft confirmed that users will be able to download Android applications on Windows and that it would be possible to install APK files downloaded from third-party sources. You can't do much with APKs on platforms other than Android unless you install an Android emulator like Bluestacks. Take the APK you want to install (whether it's the Google application package or something else) and place the file in the tools folder of the SDK directory.
But APKs power every download on your phone, so you take care of them all the time, even if you don't realize it. As already mentioned above, when you visit Google Play and download or update an application, the store automatically installs the APK for you. You can tap on the Google Play Store download for iPhone and start browsing the apps once you complete the installation of the APK file. Most Android implementations allow users to install APK files manually only after activating the Unknown Sources setting that allows installation from sources other than trusted sources, such as Google Play. While Google Play has filters to detect dangerous applications, there isn't as much protection when you install APKs on your own. It turns out that APKs are a variant of the JAR (Java Archive) file format, since much of Android is built on Java. When the application is ready for shipping, Android Studio compiles it and then places it all in one container: an APK.
To open an APK file and consider the individual files in it, you'll use an application that corresponds to the format of the extracted file.