The Protestant Reformation occurred because the Catholic church was really letting itself go and it was slipping into bad habits. Which led Martin Luther to nail a paper with all the problems of the church to the church door.
Martin Luther believed in Sola Scriptura which means the bible is all you need, Sola Fide which means good deeds do not help you become righteous, Sola Gratia which means we are incapable of doing good works, and Sola Christo which means Christ must be the sole content of the scriptures.
While Protestants and Catholics were once alike now they have many differences. Firstly, Protestants don't see the pope as God's leader on earth. They also don't believe that Jesus is fully present in the Eucharist. Most Protestants don't ask other saints to pray for them. Most Protestants also don't believe in purgatory. Lastly Protestants believe in Sola Scriptura which means the bible is all that is needed.
The Church responded to the reformation by holding The Council of Trent in 1545. The purpose of the council was to clearly define the teaching of the Church, address the abuse and corruption, and regulate the training of priests.
The Cons of the reformation was that the church became divided and Protestantism grew rapidly.
The Pros of the reformation were that if finally brought light to the Church's issues and helped them address and fix all of their problems
The Church rejected Sola Fide and affirmed that we need faith and good works for our own salvation. The Church also taught that the bible can be interpreted in so many different ways that it can't be the only thing you which is what Sola Scriptura teaches. One bible verse could be interpreted in many different ways by just putting emphasis on different points of the verse. That is why having the bible only is not sufficient enough to teach the works of Christ.