Christians often assert that the Bible says that it is God's message to humanity. I usually ignore such comments, but when someone claims to be doing apologetics, i.e., rationaly defending their faith, I think the assertion should be challenged. Any claim that "the Bible" says anything about itself assumes the faith rather than defends it. In fact, most claims that "the Bible" says anything about anything assume a conclusion that the apologist is obligated to prove first.
Claims that the Bible says something about itself assume that the Bible is a single unified message, but in fact, it is a collection of writings from different authors at different times. None of those books and none of those authors make any claims about the collection of books that we know as the Bible. Some of the authors quote other books that appear in the collection and some of them refer to other books as scripture, but none of them identifies any particular collection of books as comprising scripture, and, as far as I know, none of them identifies his own writings as being part of such a collection. The Bible never says that it is "the Bible."
How the Christians refer to the Bible when speaking to each other is certainly no concern of mine, however, when a Christian claims to be defending his or her faith in a discussion that includes unbelievers, I think that Christians need to prove that "the Bible" says anything. If they are not prepared to do so, they should limit their statements what "Paul" says or what "the Gospel of John" says.
When I have raised this objection, I have not found any Christians that are very well perpared to defend their notion that it is "the Bible" that is saying things rather than the individual books or authors. I suspect this is because they simply take for granted that the issue is whether the Bible is the word of God. They have never given much thought to what the justification might be for thinking of the Bible as a single unified document. I suspect that most have no justification or than their assumptions.