What happens to stocks in a sale or shutdown? (Inheritance)

So I was left various documents from a deceased grandparent that included being gifted 1,000 shares of his company “A” from back in the 60’s. Said company was sold to someone and it’s unclear if it still exists from my research thus far. I am not sure how to explore this discovery, mainly out of curiosity, but also as a financial opportunity if one exists. I realize the company may simply not exist and therefore the documents are purely of historical/family nature with zero cash value and that’s