YOU can trust the Bible as a reliable source on how to guide your life,also Moses had scribes. Some people are not aware of the schools of thoughts when they handed down the oral commandments.
Read the other books for yourself and you will see that they do not compare as trust worthy as the Bible. However, you will read a quote from the Book of Thomas and wonder how did he have this quote from Jesus. Well anyhow, even Jehovah says when reading about the works of the Kings is it not written in the other books? Then you can read in the 2 Kings and realize not all the accounts of the kings are in there, and etc,. However, for us today does it matter? NO because 1 and 2 kings expresses what we need to know! So read the other books as well as the false books. They are fun but I do not take them serious as holy scriptures and although John quotes from the book of Enoch and we can find the book I do not take the book of Enoch as God word and written with Holy Spirit! Recently, someone posted something about Romans 8 those other books just do not hold the love that the bible explains. They lack!
Also, historical writers are making money on these others books but if they go against the bible then it is not by HOLY SPIRT or God WORD when in fact it wrong. Sure they could have some saying of Jesus. Historical theology just wonder why some of the saying in such books are there prior to the writings of the N.T. Take the entire book and not just the a saying that is in these other books and judge for your self. In my view point they are not worth it but just fables with some truths and that is the makings of good fiction writers. They had a lot of time on their hands but I am sure a good fiction writer could have done a better job the some of these other books.
The Mormon book is fiction and does not belong with ANY books of the Bible, and anyone who thinks so suffers from some sort of delusion.