The Catholic Church did not add any books to the Bible. I believe your question is more about the difference between the Septuagint and rabbinic Old Testement scriptures.
In Jesus’ day the canon of the OT had not been settled. Different groups in Palestine honored different canons of scripture. The Sadducees and Samaritans, for example, held that only the first five books of the Bible were Scripture. The Pharisees had a canonical tradition that is much like the Protestant one today. Finally, some Jews honored the canonical tradition that is much like the Septuagint translation of the OT.
The Greek translation was made between 250-125 BC and is known as the “Septuagint” after the Latin word for 70(LXX), which is the number of authors who compiled it.
So which canon did Jesus use?? In His time Hebrew was a dead language and most Palestinian Jews spoke Aramaic, while Greek was common in the Mediterranean. So it is no surprise that all the New Testament writers used the Greek Septuagint. The vast majority of OT quotes in the NT are from the Greek Septuagint. In fact, even Protestant authors Gleason Archer and G.C. Chirichigno list 340 places where the NT sited the Septuagint, as opposed to only 33 from the Hebrew canon. That’s 90% use of the Septuagint only.
In 1529 Martin Luther proposed to adopt the Hebrew canon used by rabbinic Judaism (Those who rejected Jesus) of 39 books of OT canon. He did this because he did not like what some of the seven books had to say, like praying for the dead in 2 Maccabees.
In response to this heresy, the Council of Trent **reaffirmed ** the 73 book canon of the Bible, including the 46 book Septuagint OT. The Catholic Church did not add the seven books, but merely reaffirmed what she had established 1200 years earlier.
Would you rather use the OT used by the apostles and other NT writers, or the OT used by the Jews who later rejected Christ?
If you follow the Septuagint you follow the apostles and other NT writers. If you follow the Hebrew you follow those who rejected Jesus and Martin Luther.
Around the end of the fourth century, The Church settled the confusion and established the canon of the OT and NT with a series of councils and decrees.
382AD - Pope Damasus, wrote a decree listing the present OT and NT canon of 73 books.
393AD - Council of Hippo approved the 73 book OT and NT canon.
397AD - Council of Carthage also approved the 73 book OT and NT canon.
405AD - Pope St. Innocent wrote a letter confirming the 73 book OT and NT canon approved at Hippo and Carthage.
419AD - Second Council of Carthage also approved the 73 book OT and NT canon.
1441AD - the ecumenical council of Florence formally defined the same 73 book list of Scripture.
1546AD - the ecumenical council of Trent formally defined the same 73 books as the canon of the Bible.