The person who asked this question highlighted the contrast between Rom. 1:1 — which says the letter to the Romans is from Paul — and Rom. 16:22, which says:
I Tertius, who wrote this letter, greet you in the Lord.
In this situation, Tertius is working as Paul’s secretary, writing down the words that Paul dictates to him. The relationship between Paul and Tertius is similar to the relationship between the prophet Jeremiah and Baruch the scribe (e.g. Jer. 36:4):
Then Jeremiah called Baruch the son of Neriah, and Baruch wrote on a scroll at the dictation of Jeremiah all the words of the Lord that he had spoken to him.
The words are from Jeremiah, but Baruch is writing them down. In the same way, the letter to the Romans is from Paul, and Tertius is writing it down for him.