The below link explains how to download ADK 8.1 files for offline use. The link explains both GUI and command line methods.
About Nirmal Sharma
Nirmal is a MCSEx3, MCITP and was awarded Microsoft MVP award in Directory Services. He is specialized in Directory Services, Microsoft Clustering, Hyper-V, SQL and Exchange and has been involved in Microsoft Technologies since 1994. In his spare time, he offers technical help by writing tips and articles. Nirmal can be reached at [email protected].