If you read the Bible, you observe that the God himself did not really know much about Satan, perhaps it became clear for him in the course of time. Nameley, in the Old Testament (OT), it is not told that the figure behind the Eden snake was Satan. Try to find...
A major JW doctrine, on which everything is hung, is that some kind of a big principle has been called into question... about sovereignity between God and Satan. A funny thing is that you cannot find this doctrine defined in the in the OT.
Even vorse, in the New Testament (NT) this is not told us either and, what is told, is certainly not in the JW style. It is true that in the NT Satan lurks in here and there, but his existence does not appear as a central point in Christ's teachings in any way.
So was Jehovah so diabolic that he held this information out of reach for us for centuries? And then finally it revealed to Russell and Rutherford (hih)? In their publications Satan would then be written a bigger role than in the Bible.
The role of Satan, however, is said to be a key teaching of WT society? But then it is ONLY found in the Apocryphal texts of the OT. Just see the Book of Wisdom and the Book of Enoch. Just read those books and you find that the JW world explanation relies on information from the Apcrypha.
This explains you why JWs are not to read those texts. Reading them would make evident, where the interpretations about what happened in Eden and about Satan's role came from, and that it all reflects only the 'questionable' tradition of the Apocrypha, vhich the WT says is uninspired.
Reading list (not long): The Book of Enoch and The Book of Wisdom. Why is it that central elements of the Truth(TM) are to be found on these only?