So one of the major divisions between Catholicism and Protestantism is that Catholicism rejects Sola Scriptura, or the idea that all of our (theological) beliefs must come from Scripture alone.
Except, ironically, this belief in Sola Scriptura isn't found in the Bible...so Sola Scriptura is a self-refuting principle.
There are some folks who will cite this verse in Revelation to prove Sola Sciptura:
I testify to everyone who hears the words of the prophecy of this book: if anyone adds to them, God will add to him the plagues which are written in this book;--Revelation 22:18
That is, the Bible is complete--and "adding to" the Bible, like the Catholic Church has done, with her papal encyclicals, Church councils, infallible teachings, is condemned in the above verse.
Catholic response:if we take the above words from Revelation literally, and no one can add to that book, Revelation, then we wouldn't have the New Testament in its entirety. Revelation, even if it was placed at the end of the Bible, wasn't written last. All of the books written AFTER Revelation would then be considered "adding to" that book.
Historians record Revelation to be written about 90 AD. The Gospel of John, the epistles of John, Jude, Timothy, were all believed to have been written after that...that is, were ADDED after the inspired writing of Revelation.
Also, the Catholic Church hasn't "added to" anything. The entirety of the kerygma, the gospel message, the good news, was given, once for all (Jude 1:3), to the Church. In other words, the Catholic faith was whole and entire before a single word of the New Testament was ever put to writ. The Church received this good news 2000 years ago, and has proclaimed it for 2000 years. Some of this good news was written down (Sacred Scripture) and some of it has been proclaimed orally (Sacred Tradition). Papal encyclicals and other magisterial documents are NOT adding to the Faith--they are in-depth clarifications, insights and illuminations on what has already been professed.