What are the differences between Catholics and the Jehovah's Witnesses What the are differences and similarities between Jehovah's Witnesses and Catholics? 

To what extent is the official bible accepted by the Catholic church different from the official JW translation?

Are there any differences in the most important dogmata?
At the most fundamental level, Roman Catholics subscribe to the Nicene Creed, Jehovah's Witnesses do not.  (JWs would call the Creed itself heresy, so this is not a slam.) This means that unlike 98% of the world's Christians, Jehovah's Witnesses deny such things as:


The Trinity
The Divinity of Jesus
The Nature of Salvation
The Communion of Saints / The Role of the Church


and many, many more things.

Additionally, the Jehovah's Witness subscribe only to the New World Translation of the 66 books Protestants put in the canon.  This translation is considered faulty by most Nicene Christians for translations such as:


John 1:1,


  In the Beginning was the Word, and the Word was with God, and the Word was a god



This implies that God is one god amongst several to Nicene Christians - something that Nicene Christians would reject.


John 10


  I and the Father are One in Unity



This addition is an attempt to reject one of the most obvious prooftexts of the Trinity. As Nicea is explicitly Trinitarian and this is not, it likewise excludes JWs from that category.


Christologically, JWs are essentially Arianist, meaning their Christology also differs.


When most people think of "Christianity" they are thinking of Nicene Christianity. It is entirely fair to say then that Roman Catholics are what most people consider "Christian" and Jehovah's Witness are not.