The Torah is a document which was given in a miraculous manner to approximately 2.5 million people simultaneously. These people and their descendents have transmitted it verbatum, and have attested to the Divine revelatory nature of this document down throughout the generations until today. That in fact makes it the most reliable document of its nature, since all other documents claiming divine origin were only handed down by one “prophet” (eg Mohamed, Jesus, etc…). I have never even heard anyone ever refer to another possible source for it, because it’s source was so clearly documented and attested to in an unbroken chain of tradition.
There is much more that I could answer on the subject, and if you wish to hear more, let me know.