Communication between UWP and Non UWP app

I recommend the following sample by stefanwick. It's actually 4 parts with details and samples in code and in windows store: https://stefanwick.com/2018/04/06/uwp-with-desktop-extension-part-1/

Yes, non-UWP apps can use AppServices to communicate with UWP apps.

There is a sample here: https://github.com/Microsoft/DesktopBridgeToUWP-Samples/blob/master/Samples/AppServiceBridgeSample_C%2B%2B/cs/Win32Process_CPP/Win32Process_CPP.cpp