Paul is the only figure in the New Testament from whom we have documents he wrote himself, and this makes him the best-evidenced person in the first Christian generation, but the collection under his name is not all his, and the division matters.
Seven letters are accepted as authentically Pauline across the scholarly spectrum, including by conservative and confessional scholars: Romans, First and Second Corinthians, Galatians, Philippians, First Thessalonians and Philemon. They date to roughly the fifties, which makes them the earliest Christian writings in existence, earlier than any Gospel by a decade or two.
Six more are disputed on grounds of vocabulary, style, theology and situation. Ephesians, Colossians and Second Thessalonians are contested; the three Pastoral Epistles, First and Second Timothy and Titus, are regarded by a large majority of critical scholars as later, written in his name by admirers. Pseudonymous writing under a revered name was a normal ancient practice and was not necessarily understood as forgery, though some ancient writers plainly did object to it. Hebrews was attributed to Paul for centuries and is anonymous; Origen said in the third century that who wrote it, God knows.
This division is not a marginal technicality. The instruction that women should keep silent and not teach is in First Timothy, a disputed letter. Household codes ordering slaves to obey masters are in Ephesians and Colossians, both disputed. Meanwhile the undisputed Galatians contains the line that in Christ there is neither Jew nor Greek, slave nor free, male nor female. Which Paul a reader meets depends on which letters they are handed.