Make appx package for Windows Store downloaded app

Can anybody help me make an appx package for a Windows Store app that I have installed on my computer. I have all the files, signatures, etc. for the app. I just want to make an appx package for it so that I can sideload it to other Windows 8+ PCs. Anyone know how to?

Search MSDN for App Packager. MS has a tool that will package it all for you.

It won’t work for me, I don’t know why. It says that there are errors in the AppxManifest file when I just downloaded the app from the Windows Store itself. Any alternatives to it or am I doing something wrong?