Source: Catholic Answers
Is it true that at Trent the Church added the seven Deuterocanonical books (Judith, Tobit, 1 & 2 Maccabees, Wisdom, Baruch, and Ecclesiasticus) to the Bible ?
No. The Council of Trent (1545-1564) infallibly reiterated what the Church had long taught regarding the canons of the Old and New Testaments. Pope Damasus promulgated the Catholic canons at the Synod of Rome in A.D. 382, and later, at the regional councils of Hippo (393) and Carthage (397, 419), the Church again defined the same list of books as inspired.
The canons of the Old and New Testaments, as defined by Pope Damasus and the Councils of Hippo and Carthage, were later ratified (though the books were not enumerated individually) by the later Ecumenical councils of II Nicaea (787) and Florence (1438-1445). Although the Council of Trent, in response to the Protestant violation of the Bible by deleting the seven Deuterocanonical books plus portions of Daniel and Esther, was the first infallible conciliar listing of each individual book, it certainly did not add those books to the canon.
If that were the case, how could Martin Luther and the other Reformers have objected to the presence of those books decades before the Council of Trent if they weren't in the canon to begin with and were added by the Council of Trent?