To download APK files you will need an Android device as APK file is an installation package of a program for Android system. This is because an APK file is an application that is meant to run on specific devices only, unlike other file types like AVI or PDF that work on multiple platforms.
Instead, if you want to convert your APK file to ZIP, you'd use the instructions explained on the Apkpure.download website. Either open the APK file in a file extraction tool and then repackage it as a ZIP, or simply rename the .APK file to .ZIP. Renaming a file like this is not how you convert the file. It only works in the case of APK files because the file format is already using ZIP but it's just appending a different file extension (.APK) to the end.
Like already mentioned above, you cannot convert an APK file to IPA for use on iOS, nor can you convert APK to EXE to use the Android app in Windows. However, you can normally find an iOS alternative that works in place of the Android app that you want to be installed on your iPhone or iPad. Most developers have the same app available on both platforms (both an APK for Android and an IPA for iOS).
As for the APK to EXE converter, just install a Windows APK opener from above and then use it to open the Android app on your computer; it doesn't need to exist in the EXE file format for that to work.
Best android APK you can download at Apkpure.download: