Question:
Answer:
The Protestant Reformation affected Catholics in several ways. For example, the Catholic Church further elaborated and clarified its teaching through the ecumenical Council of Trent, including re: the sacraments, how we are saved, and Sacred Scripture. This enabled Catholics to better know and live their faith.
In addition, reforms were made, including stopping ill-gotten gain re: the abuse of indulgences.
And because of the significant defection of Catholics to various forms of Protestantism at that time, it led to the redoubling of efforts re: the Church’s Great Commission received from our Lord (Matt 28:18-20). That mission continues today, not only in striving to bring our separated brethren into full communion but also preaching Christ and his Church to all non-Catholics (see CCC 846-48).
For more on the Council of Trent, see this link to the conciliar documents. And for additional information on the Reformation, read this article and this article from Catholic Answers.