You are downloading the Briefcase APPX file v188.8.131.52 for Windows Phone. Briefcase is a free and useful Utilities & Tools app: Briefcase is a free file manager app. The app has a capability to manage local files, memory card and OneDrive files. The app has following ... You can now download the offline APPX file to install & try it.
Download Locations for Briefcase 184.108.40.206 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 Briefcase APPX file, move the file to your phone's SD card and then tap 'Install local apps' in the phone's App list.