Is it true as some say that apostle Paul invented Christian faith or he was a roman agent and only pretended to believe in Jesus?

No. Paul (Saul of Tarsus) was an enemy, working for the Sanhedrin, set out to kill the Christians, but had an experience with Jesus personally on the road to Damascus. He spent a lot of times with the apostles of Jesus, and even they believed him and accepted him. He ended up suffering a lot for the cause of Jesus, and was eventually beheaded by Rome for the testimony of Jesus. He did not work for Rome, but was a Jew, that had Roman citizenship, as he had a house in Rome. The apostles did not preach contrary to Paul. Read the book of John...etc... they are in agreement. Paul did not invent Christians, as the Christians (followers of Jesus) existed, even before he began his persecutions of them.

Saint Paul, with some initial conflict, was duly accepted by the leaders of the Church that Jesus personally founded.

No and no.

The evidence: the Pauline epistles found in the Bible.

The evidence is there in the New Testament. Read it for what it says and it becomes clear.

There is no evidence in the word of God/ the Holy Bible that support that notion, in fact quite to the contrary. Abram was the first to practice faith in God, thousands of years before Saul was even born. And Jesus preached and taught faith when Saul was still persecuting the Jesus and His followers. However, Saul was used mightily to spread the Gospel of Jesus Christ once his eyes were opened and he converted to Christianity and became Paul the apostle. 

Jesus was the founder and leader of an exclusive Jewish sect, you HAD to be a Jew to join up. After the crucifixion, Peter insisted that this strict tradition be kept. It was Paul who opened the floodgates to let pagans in because he saw a political advantage in uniting all of the Roman Empire under one faith so it would be easier to control

Paul did invent christianity.  Just look at the teachings of Jesus.  Jesus was a JEW and taught nothing but JUDAISM.  he never even hinted at starting a new religion.

Paul is the only one who taught the new religion bassd on Jesus in the Bible.  

I don't know if he was a Roman agent or not. 

Christianity was certainly invented by Paul.

Paul neither invented the Christian faith nor was he a Roman agent.