You are downloading the StackCook AppXBundle file v2015.1027.104.0 for Windows Phone. StackCook is a free and useful Education app: The StackOverflow app you are looking for on Windows Phone. It’s a native app on Windows Phone unlike a wrapper on StackOverflow website. The ... You can now download the offline AppXBundle file to install & try it.
Download Locations for StackCook 2015.1027.104.0 AppXBundle file
To try to install it manually from an SD card, you should choose one of the server location above to get the offline StackCook AppXBundle file, move the file to your phone's SD card and then tap 'Install local apps' in the phone's App list.