Briefly, my son is newly away at college and has informed me that he is thinking of converting to Mormonism. I would like to know the Catholic Church’s formal view on converting to another religion and also its view on proselytizing.
The Catholic Church does not want any of its members to leave the Church, especially through apostasy to a non-Christian religion such as Mormonism, and takes a dim view of techniques intended to manipulate the vulnerable (such as a newly-independent young adult starting college) into rejecting his religious and spiritual heritage.
What the Church thinks about conversion and proselytism seems to me to be the least of your concerns right now. Your son’s interest in Mormonism and how to address it should be paramount. In addition to reading the books linked below, you may want to reassess whether it is still in your son’s best interest to be “away” from his family at a place where his faith is under attack. Perhaps the suggestion that he is evidently unprepared to be trusted with the responsibility of independent living at a far-off campus might motivate your son to reconsider his involvement in Mormonism.