APK files themselves are not harmful. The Google Play Store downloads an APK Store and installs it on your device. However, it's essential to consider where the APK file was downloaded from. If an APK file is downloaded from a reliable source, such as the manufacturer's website, it's generally legal and free of malware. Installing an . APK file from an unknown source can be risky, as it may contain malware or other harmful software. It's generally recommended to only install . APK files from trusted sources such as the Google Play Store or other reputable app stores.