There are several versions and it's one of them: They're shooting it in December. That will be a final version of the movie.
But if you mean that very version, you should use the definite article:
- Which version is he talking about? - The final version.
So you get:
- What are you doing?
- I'm preparing/composing/working on a final version/draft of the contract with XYZ.
- I thought John had sent me the final version of the statement but it turned out that it was just a draft.
I hope I'm right.
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