There is a way to install unsigned .Appx App Package with PowerShell in Windows 11/10. Use the Add-AppxPackage command line to get it done easily.

Looking for File Association Fixes? Fix File Associations with File Association Fixer for Windows 7/8 & Vista, in case you find that you are unable to open particular files.

Microsoft Windows 8 to include new AppX PDF reader April 4, 2011 - 8:40 pm Eat your heart out Adobe, there is a new PDF reader in town.