Paul is actually speaking of himself as if he were speaking of someone else, but this should be translated literally if possible. Paul now defends his authority by telling about a wonderful vision of heaven. Although he speaks in the third person in verses 2-5, verse 7 indicates that he was the person who experienced the vision. It was so great a vision that God gave him a physical handicap to keep him humble.
# whether in the body or out of the body, I do not know
Paul continues to describe himself as if this happened to another person. "I do not know if this man was in his physical body or in his spiritual body"
Many scholars believe the "third" heaven is the dwelling place of God. This is because Scripture also uses "heaven" to refer to the sky (the "first" heaven) and the universe (the "second" heaven).