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There are some smaller countries like Costa Rica and Panama that have their own currencies but also use the US dollar as an official currency alongside it and there are some countries that have a their currency pegged to the US dollar such as Saudi Arabia(this might be a better option actually, though I don't know how they enforce that).
Argentina adopting the USD would push the USD up as there would then be more demand for it. Though the degree it would do so is probably negligible given that it's already the global reserve currency and the currency of the largest economy on earth, so the increased demand from Argentina would probably be like a drop in the ocean.