“Then Saul, (who also is called Paul,) filled with the Holy Ghost, set his eyes on him,”
King James Version (KJV)
13:9 Then Saul, who was also called Paul - It is not improbable, that coming now among the Romans, they would naturally adapt his name to their own language, and so called him Paul instead of Saul. Perhaps the family of the proconsul might be the first who addressed to or spoke of him by this name. And from this time, being the apostle of the Gentiles, he himself used the name which was more familiar to them.
Ac 13:9 But Saul, (who also [is called] Paul). From this date he is the chief figure of the Acts. Barnabas, who had hitherto been the leader, falls behind. The origin of the name Paul is unknown. It is a Roman name, that of a great Roman family, and it is likely that the great apostle had two names, one Jewish, the other Gentile, a common thing anciently. Peter (Mt 16:16), Daniel (Da 1:7), Esther (Es 2:7), and many others afford examples. Filled with the Holy Ghost. Acting under the impulse of the Holy Spirit.