So, I just finished installing Pac-Rom, which is great. However, I've run into a huge problem. Custom Roms don't come pre-loaded with the Google Play Store, and I'm supposed to install something called gapps in place of it. The issue is that my phone refuses to open up apk files. I've tried downloading gapps, as well as amazon app store, and haven't been able to open their apk files. To my knowledge, any app I download online will come in the form of an apk, so I don't know how I'm supposed to get around this. Any suggestions will be greatly appreciated.