Alternatively, enable developer mode if you plan to do UWP app development. For most users that do not intend to do UWP app development, developer mode will not be necessary.
Install the *.cer file into Local Machine -> Trusted Root Certification Authorities
This will require administrator elevation. If you installed the certificate and did not have to elevate, you likely installed it into an incorrect certificate store.
double click the *.appxbundle
Optional: Install Context menu integration from here