Catechism of the Catholic Church §36 — excerpt
"Our holy mother, the Church, holds and teaches that God, the first principle and last end of all things, can be known with certainty from the created world by the natural light of human reason."
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: Vatican Council I, Dei Filius 2: DS 3004 cf. 3026 · Vatican Council II, Dei Verbum 6