I am new to Wix and this is what I am trying to do. I need to throw a message if I detect the same application is already installed. I want to find that out using its registry entry

I have a wix3 installer which install the main software together with a third party software.
I would like that the third party software could be installed optionally. The Yes/No installation dialog for this third party software appears but is I set “no” the whole installation is aborted.

An old installer script I have inherited has the following peculiar behaviour I’d like to clean up:

I’ve created a Wix installer that installs some of our software and copies two .msi files (3rd party products) into the install folder.