Protestant
Did the Church add books to the Bible?
The Catholic Old Testament did not gain books; rather, Protestant Bibles removed seven books (the deuterocanon) that had been read as Scripture by Christians for over a millennium, following a sixteenth-century decision to match a later rabbinic Jewish canon.
Catholic teaching
The Church did not compile the canon by private judgment; she recognized, under the Spirit's guidance, which books had always been used as inspired Scripture in the Church's worship, affirming a 73-book canon at regional councils in the fourth century and dogmatically at Trent in response to Reformation-era removals.
Biblical foundation
The New Testament itself quotes and alludes to the deuterocanonical books (compare Hebrews 11:35 with the resurrection hope in 2 Maccabees 7), and Jesus and the apostles used the Septuagint, the Greek Old Testament that included these books, as their working Scripture.
Scripture references
Historical evidence
The Councils of Hippo (393) and Carthage (397, 419), confirmed by Pope Innocent I, listed the same 73 books later reaffirmed at Trent, while Martin Luther moved the deuterocanonical books to a separate 'Apocrypha' section in 1534, a novel editorial decision unmatched in the prior 1,500 years of Christian usage.
The Church Fathers
“The whole canon of Scripture...is contained in the following books... Tobias, Esther, and two books of Maccabees.”