Moses' Use of Written Sources

We talk about the essential Mosaic authorship of the Pentateuch. Are we to envision Moses sitting down and writing everything firsthand? Or are there any examples of him using written sources in the Pentateuch? And I think there are. If you turn to Genesis 5:1, we're told this is the written account of Adam's line, so it does seem that Moses here is reflecting on some sort of written document that he had before him. And then later on in the book of Numbers, okay, and the account is the journey to the plains of Moab, we're told in Numbers 21:14, "That is why the Book of the Wars of the Lord says," and he quotes from this thing called the "Book of the Wars of the Lord." Now, we don't have any extant copies of that, but it looks like Moses did indeed have written sources at his disposal when writing the Pentateuch.