As a Protestant I've heard and read many teachings on why we can be confident that the Bible is God's Word. And I've taught it myself. You haven't been out much if you think the RCC has a monopoly on the topic.
Irenaeus -- "We have learned from none others the plan of our salvation, than from those through whom the gospel has come down to us, which they did at one time proclaim in public, and, at a later period, by the will of God, handed down to us in the Scriptures, to be the ground and pillar of our faith."
Basically as early as the 2nd century Irenaeus and Tertullian were teaching Apostolic Tradition, and once the apostles wrote it down as Scripture it's the ground and pillar of our faith. Neither Irenaeus nor Tertullian said to abide by tradition that was not written down as Scripture. In other words, tradition not written into Scripture doesn't qualify as the kind of "tradition" they said as the ground and pillar of our faith.
Funny; that's not what the Bible says. It is the Church -- not Scripture -- that is the pillar and ground of the truth. 1 Tim 3:15.
Neither Irenaeus nor Tertullian said to abide by tradition that was not written down as Scripture.
Didn't they? Funny; the Bible does. 2 Thess 2:15. And elsewhere.