Someone who does not believe the Bible is the Word of God, from God, can NOT be a believer. Before Christ saved me, I was reading the Bible. It wasn't even that I did not believe it, so much as I did not understand it. Many times, people don't understand what they are reading, so they say it is because men wrote it.
As I read the Bible before I was saved, I had circles and question marks on every page. After God saved me, I began to re-read those pages. I realized it was all about Jesus! I had met the author of the book.
You can examine all the evidence and you will find the truth in every story, parable, moral and words of wisdom. The Bible is true. But, if you don't believe in Jesus, I could prove every page was true, and you still would not believe it was true, because you would not have met the author.
The Bible is not just about right and wrong, how to behave, although that is certainly there. Instead, it is the revelation of Jesus Christ, from start to end. If you read it you will find Jesus in every page. Someone who says the Bible is written by men, is certainly not seeing God's message to us - and that message is Jesus.
Once you have Jesus, you can study the Bible more. The Holy Spirit will lead you in all truth. The Holy Spirit comes and fills our hearts and lives, when God saves us. Without the Holy Spirit, you will have no truth, and a lot of error, like your friend.
In passing, I read the books of all the other religions before I was saved. I also deeply looked into them! They were all man-made! There was no inspiration from God. Just rules and regulations, and make your own way to God. Which I realized I would never be good enough to make it to God on my own.
Christianity is different! The Bible was not written by holy men, long dead and buried. Well, true, the prophets put down the actual words that God inspired them to write! Christianity is about the living God, risen and alive! And the Holy Spirit who was sent to us. And the Word of God that was left to lead and guide us!
No other religion has a living God and Saviour, a Holy Spirit who comforts, encourages and teaches us, and a true and inspired book, confirming who Jesus is, and that he came to save us from our sins! Do not doubt what you believe. Dig into the evidence, if it helps a bit. But mostly, draw closer to Jesus and he will show you his truth, and that the Bible is true, and inspired by God!