Within the book of Acts it has more then one author clearly...as half way through the names change instead of Simon (stone) peter, it says "whose surname was"...that is incorrect as it was a given name, not a surname...it was given as a stone of stumbling to all who follow his teachings of man (so binding), and not the things of God..

There are quite a few slips in names changes also....so clearly someone started recording it and then the end points and facts that only Paul would have known and possibly Timothy when told by Paul them things; who was one of Paul's accomplices...

As Paul mentioned in one of his letters, bring the other scrolls and so in that I do believe he meant the record of Acts, and any other documents he got his hands on.