Apkpure and most of such websites such as apk-dl and apkmirror, simply download the apps from the Play Store and then upload the APKs on their websites. So, they are safe.What is the best site to download apk files?
Website: https://apkbucket.net/ APK Bucket is amongst the best APK sites which is not just a platform to download the given apk files on the site but it is much more than that. The site is an online APK downloader which can download any app through its package ID or Google Play URL easily.How do I find an APK?
If you want to know where your apk files are stored, open a emulator and then go to. DDMS>File Explorer-> you can see a directory by name "data" -> Click on it and you will see a "app" folder. Your apks are stored there. In fact just copying a apk directly to the folder works for me with emulators.