ALL Android Apps have a Linux File extension of *.apk......... On cellular phones and tablets, only the Android OS can decode an apk file....
HTC HD2 is a windows mobile phone... the win OS uses *.cab files for apps.... obviously, cab and apk are like USA and Chinese lanuages and fonts... COMPLETELY DIFFERENT!
In order to use apk, you MUST have android! You can put Android OS on your HD2... Many people have done this!!!!!!!!!!!!!!! IT require hacking and wiping your phone... if your confortable doing this, then see XDA Developers and/or Android Central.com for details.... once you have flashed over the Android OS ROM and installed it on your HD2 to completely replace the Windows OS, only then can your get apks.... good luck!
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