I\'m just starting to learn how to use WiX and I\'m running into a snag. My package uses a third party library that requires some file to exist both in the GAC and the package
I found the post - which has since moved, the new URL is here: https://devblogs.microsoft.com/setup/installing-assemblies-for-runtime-and-design-time-use/
In essence, you create 2 components, the GAC one into a new folder which is basically ignored, as it will go to the GAC, and another component to the place you want to copy to - just without the Assembly=".net"
property.
The below example is from the code, and I've got it working in my project using this technique.