The company was founded by a man who has/had been to Paris. What form should be used and why?
The company was founded by a man who had been to Paris [before he founded the company; this man can be still alive or already dead].
The company was founded by a man who has been to Paris [the founder is still alive; the fact that he has been to Paris is considered important in relation to the moment of speech: this is not someone who has never been to Paris; the moment of his going to Paris is not specified, it can be before or after the foundation of the company].
So depending on what you want to say, chose an option that suits best.