Didn’t Moses pen the first five books?
Moses probably didn't have a pen :-) OTOH, Joseph was stuck in the pen for maybe seven years...
Whatever Moses wrote in those books, he did by the same Holy Spirit inspiration as all the other prophets of the Lord. There is no way Moses could have known all the things that Genesis, for example, relates except by the leading of the Holy Spirit. He wasn't there at the start of creation or in the Garden of Eden, when Adam and Eve walked with God. Moses lived nearly a thousand years AFTER Abraham walked the earth. Just as the Holy Spirit moved the writers of the New Testament books to write about things they could not have known about personally (i.e., what Jesus prayed in the garden the night He was betrayed), so that same process went on for the writers of the books in the Old Testament. It is because the Holy Spirit was working in these prophets, we can have assurance of the things we are told in Scripture and trust in things God has made known to us through His sacred word.
Moses wrote scrolls shortly before his death. That was some 40 years after the experience at Sinai.
Obviously there was communication from God without a book.