Do Jehovah's Witnesses have their own version of the Bible? What is their reason for not accepting other versions such as the NIV or the KJV?
Yes, they do. It's called New World Translation.
There are several verses with a completely different meaning than other translations, such as John 1:1
Quite different than the NIV translation
The difference is easy to see when you consider how it affects the doctrine of the Trinity, Christ's identity, and the idea of a single God vs. the idea that the word was "a god" - separate from The God.
Other, commonly accepted translations agree with the NIV translation.
The argument I've heard time and time again is that the Bible has been corrupted over time, intentionally, or not, and that they, the one true Church, have the only accurately translated version. (This was from three personal friends, all JW, and from several missionaries that I spoke with. I don't have official statements from the Watchtower Society claiming this.)
There are more differences, along the same vein, but I don't wish to get into a discussion on the validity of their claims vs. those of other denominations. Such discussion would be off-topic and frowned upon.
I included the above, only to show that the NWT is more than a slightly differently translated version. Most of the passages are the same,but those few that are different significantly alter the meaning relating to some foundational doctrinal views held by more (traditional? mainstream?) denominations.
Jehovah’s Witnesses use the standard 66-book Protestant Bible, but usually use their own translation thereof (they do reference other translations from time to time, but generally use The New World Translation). It’s fair to say that the NWT is quite, let’s say, distinctive in places, and has received a fair amount of criticism. The Witnesses do not in any way claim that the translation of the NWT was inspired by God, and are happy to argue their doctrines from other translations if you ask them to. (Indeed, they did so for many years before the release of the NWT, and continue to do so in languages which do not yet have a version of the NWT.)
Here are some of the distinctive features of the New World Translation.
In general, the footnotes and appendices in NWT Ref are about the mechanics of translation, not theology. They are about tricky linguistic points and textual variants.
Yes we have our own bible that we use, but we sometimes do study and compare with other bibles. I myself have an old pre 1985 King James that still has the name Jehovah in it, as well as 5 other translations (not counting internet access to many more)
The reason we don't use the king James version anymore (used to be the bible the witness used) Is because we have an easier to understand bible with Jehovah's name restored to it. The old English from the KJV has been rendered in modern English so that the reader can better understand the scriptures. The reason for the NWT is in the forward at the beginning of the book that can be read here for free.
As for the NIV that was made/copyrighted 1973 . By that time the Watchtower society had produced and copyrighted our bible by 1961, so naturally we where using that.
Source for dates of copyright is found in the front of my New world Translation and the NIV copyright was found here