If it is relevant and either not hearsay or a hearsay exception, and you got a certified copy from the court, yes,. You could use it to impeach the person who gave it if that person was present as a witness. You don't impeach affidavits, you impeach people. If start using exhibits attached to the deposition, then you are looking at evidence within evidence, you would have to consider it all in the context of your trial. Evidence is tricky. But you are certainly way ahead of the game with a deposition. However, you are going to have to get a certified copy from the court, you can't take it off of a website.
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