An APK file is a software package designed and developed for the Android operating system. It is not compatible with iOS, and you can only install apps purchased from the Apple App Store. Installing APK files on your iPhone is impossible, 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 best way to run a specific app on iOS is to search for the app's iOS option and get it from the Apple store. However, you can convert an APK file to ZIP or JAR files by simply changing their extension. And then you can open that file with WinZip, WinRAR, and other similar applications.
You can also install a third-party application called “APK Downloader” to open APK files on your iPhone. It should be noted that APK files do not open for iOS because they are not for this operating system and, in fact, IPA files are files suitable for iOS, and you should use those files. 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. You can't open or install APK files on an iOS device (iPhone and iPad).
After that, you will easily convert the APK suitable for Android systems into a file suitable for iOS and use it. From a legitimate website via APK, you can download applications and games that are still in beta or that are not available in your location.