Other contributors have said "What book and chapter discusses Saul's tranformation to Paul?" is the same question as "Where in the Bible does Saul become Paul?" If you believe that these are not asking the same thing and should be answered differently, click here
He had the Hebrew name of Saul and the Roman name of Paul from childhood, he may have chosen to go by his Roman name in view of his commission to declare the good news to the non-jews.
The conversion of Saul happens in Acts 9. Starting with verse 17: Then Ananias went to the house and entered it. Placing his hands on Saul, he said, "Brother Saul, the Lord - Jesus, who appeared to...
(Acts 9:3-22) 3 Now as he was traveling he approached Damascus, when suddenly a light from heaven flashed around him, 4 and he fell to the ground and heard a voice say to him: "Saul, Saul, why are...
Yes. Paul's original name was Saul of Tarsus. He changed his name after divine revelation showed him the truth of Christ. Name changing was a common practice back then.