No, he didn't
Joseph Aloisius Ratzinger is the birth name of Pope Benedict XVI.
Pope Benedict was born Josef Alois Ratzinger.
If you are referring to Joseph Ratzinger, the father of Benedict, he was a police officer. If you are referring to Benedict, before he was pope he was a cardinal and member of the Roman Curia.
Popes do not choose a surname when elected to the papacy. Before elected, though, Benedict XVI's name was Joseph Ratzinger.
His full name is Joseph Aloisius Ratzinger.
Pope Benedict was the son of Joseph Ratzinger, Sr., and Maria Ratzinger (née Peintner).
Pope Benedict's real name is Joseph Ratzinger.
Pope Benedict XVI, who is now retired, was named Joseph Alois Ratzinger.
Joseph Alois Ratzinger was the third and youngest child of Joseph Ratzinger, Sr., a police officer, and Maria Ratzinger (née Peintner).
Joseph Alois Ratzinger.
Joseph Alois Ratzinger.
I assume you mean the current pope. His birth name was Joseph Aloisius Ratzinger.