Windows RT, the only edition of Windows 8 for systems with ARM processors, only supports applications included with the system (such as a special version of Office 2013), supplied through Windows Update, or Windows Store apps, <answer>to ensure that the system only runs applications that are optimized for the architecture</answer>. Windows RT does not support running IA-32 or x64 applications. Windows Store apps can either support both the x86 and ARM architectures, or compiled to support a specific architecture.
Why does Windows RT only work with apps included with the system?
to ensure that the system only runs applications that are optimized for the architecture