I can't open my apk file

I downloaded an apk from the web that is a paid app in the Play Store, but I can't use the app cause the app knows I downloaded it without paying. I tried it with 2 different apps and these happened: First worked for a few seconds until it crashed and wouldnt let me open it. When it did open, it asked for a verification through email then crashed again. Second app isn't in the Play Store anymore, but apk versions still exist. When I downloaded it and opened the app, it asked me to download from the Play Store but it isn't in the Play Store anymore. I have Lucky Patcher on my tablet too. I was wondering if it could help or is there any alternative. Or its just impossible?