Windows8 allow offline installation of applications from pendrive?

A local computer service person just called me to know whether I'm interested in Windows 8 desktop version that he was offering for Rs.500(approx $8). I'm so curious about it. But did win8 allow offline installation of apps or i need to buy from only official windows app store just like in iOS? And if I try to download from official store will it recognize my version is pirated?