Evozi, an Android app developer, offers a one-click online APK download app that lets you download the APK installed of any Android app that's listed on the Google Play Store. the downloader app can be accessed at pai.evozi.com.
To get started, enter the web URL of any app listed on the Google Play Store and click the "generated download link" button. the APK download app will fetch the APK file from the Google Play Store and will host it on its own servers from where you downlaod the file.
Since the APK files are directly fetched from the Google Play store, it's unlikely that the Android app will be infected with any malware. also, to prevent app piracy, the APK downloader only lets you download free apps and games from the Google Play store, not the paid ones.
Http://www.labnol.org/internet/download-apk-from-google-play/28303/
How to download APK files from Google Play Store