actually, and not to step on any toes; but that verse simply means adding to the words of the prophecy contained in Revelation. When Revelation was written, there was no bible as we know it today; so the context is merely for the prophecy and the book of Revelation itself.
We add to scripture when we add our own understanding to it in sermons, prayers, and more. We are growing with God as we read the word, no new doctrines are created; but we grow as we adapt the living word to our daily lives. The prophecy of Revelation - indeed the whole book itself, is one of great mystery and it is the mystery of the prophecy that John warns the reader to not add anything to it that isn't already there.
However, if you're referring to new words found in the Book of Mormon, you won't find a verse in the bible that says you can't have a book like it - because the bible itself is not really the Word of God. What is the bible? It is a collection of books from many different authors - all inspired by God; and the proof of this inspiration is found in the accuracies of doctrine, the accuracy of prophesies, the accuracy of reporting historical events, and so on.
The Book of Mormon though, I can say, can not share in those claims like the books we find in the bible do. First off, there are no historical accounts of Nephi or other peoples mentioned in the Book of Mormon. This book was written in a time of yet-undiscovered country so the claims of a civilzation could not be investigated. However today, unlike what we find from biblical accounts of Israel and such, we don't find any archelogical evidence that any of the peoples and groups mentioned in the Book of Mormon ever existed at all, let alone do the areas and places mentioned exist. On this first charge, of which the bible passes with flying colors; the archeological and historical accuracy of the Book of Mormon falls flat so hard that it becomes a joke to continue testing it for Godly inspiration.
Next, the doctrines of the Book of Mormon have changed several times since it's first writing. I believe there have been several versions written of the Book of Mormon over the last hundred years to correct these doctrines. This charge, of which the bible passes with flying colors; leaves the Book of Mormon to be a more fictitious and imaginitive piece of literature than a reliable source of even congruently consistent philosophical truth.
Many prophecies found in the Book of Mormon are far too vague to be specific to test; unlike the specific prophesies we find in the books of Isaiah and Daniel of the bible.
In all, the Book of Mormon is good fiction; as it is not based on even the remotest legends or historical truths, it has been rewritten over a hundred years, and its wording is far to vague in most cases to be considered of any use to one studying its divine inspiration.