Since the official Windows Phone Store is closed, you must source your files from trusted community archives. :
Curiosity pulled him to his desktop. He wanted to preserve the apps that had once made the phone feel like new. He’d read that Windows Phone apps came as .xap or .appx files, packages that could be copied and stored. It wasn’t a scheme to pirate software — Noah simply wanted backups for a device the manufacturer no longer supported. download windows phone apps xap appx files to pc better