You are downloading the Unity Offline Manual AppX file v220.127.116.11 for Windows Phone. Unity Offline Manual is a free and useful Books & Reference app: An offline document app for Unity Manual v5.2.You can install the app on you Windows Phone, Surface and other devices, then you can read, learn ... You can now download the offline AppX file to install & try it.
Download Locations for Unity Offline Manual 18.104.22.168 AppX file
Important Notice: Now Due To Unspecified Limitations, You Can Not Use The Offline AppX File To Install It Any More.
To try to install it manually from an SD card, you should choose one of the server location above to get the offline Unity Offline Manual AppX file, move the file to your phone's SD card and then tap 'Install local apps' in the phone's App list.