Do this if you want to manually extract the Roslyn / CodeDom install package from the latest Dnn Release. 

This is meant for system admins who wish to install C# 7.3 as instructed for the 2sxc 17 Upgrade, but prefer to get the download file directly from the source. 

Note: If you have Dnn 10 you don't need to do this. 
If you have Dnn 9.11+ you can also skip this and install the package directly from the extensions. 

Steps

1. Download the latest releases of Dnn
2. Extract the zip
3. Go to the subfolder \Install\Library
4. Take the file Microsoft.CodeDom.Providers.DotNetCompilerPlatform_03.06.00_Install.resources
5. Rename the file to .zip
6. install the extension