Protestants say that Catholics “added” seven books to the Old Testament. In fact, Luther even argued that seven New Testament books were not inspired, and rejected all doctrine from those seven books. (Modern Protestants have uniformly restored the seven New Testament deuterocanonicals to their bibles, so this has been forgotten largely.) Catholics assert that they have always been part of the canon. And indeed, they were universally read as scripture in masses (the Catholic test of what is scripture) since the first century. I'm guessing that you meant to say the OLD Testament deuterocanonicals/apocryphal books? There are additional points that you err on as well. Here are a few links to help on that:
Luther on the Canon
The Formation of the New Testament Canon
The Apocrypha are not Canonical
No, I meant Martin Luther removed seven NEW TESTAMENT books (1-2-3 John, James, 1-2 Peter, Revelations) from his canon, but these NEW Testament “deuterocanonicals” were added back in.