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The book of Enoch was one of the books written during the Roman period in Judea, or a little before... LONG after the five books of Moses had come to be considered holy and canonical. These later books were called the Pseudopigraph* because their authors pretended that their books had been written by biblical figures. The Rabbis of that time never considered the books holy, and never included them in the Hebrew Bible. There are at least two other books written for Enoch, and all were written centuries after his life span. There was a point when these apocolyptic stories had some influence, and might have made an impact on the New Testament, but they've never been meaningful to Judaism. There are actually a few books that aren't considered holy that were pretty influential on Jews, but this isn't one of them. The "lost book" theory is mainly popular amongst the Jews for Jesus jet set.

* I could be mistaken, and the Book of Henoh (Enoch) might be part of the Apocrypha instead. Also - Another book that deals with the supernatural after world is the Book of Jasher.