A person that has been properly baptized in a non-Catholic Christian Church cannot be baptized a second time upon entering the Catholic Church. Sins subsequent to baptism are normally forgiven through the sacrament of confession in the Catholic Church. This is our formal method of repenting and seeking God’s forgiveness through admission of our sins and some form of penance. Conversion from Protestant to Catholic, in and of itself, will not bring God’s forgiveness for individual sin.
I hope this helps.
