How do stocks work?

[glatt]

I was going through my father-in-laws papers as part of his move, and found (in a shoebox of old letters and photos) 3 certificates of stocks he bought in Pepco a couple decades ago. I think he has no idea he has these, since he made no mention of them when going over finances.

So the question is, if I want to convert these certificates into a check in his name how do I do that? I've never seen one of these certificates in person before. Each one shows the number of shares he bought, and what their price was on the date of purchase. Do I get him to sign the back, and then take them to Pepco, or do I find a stock broker to buy them? Just what do you do with these pieces of paper? Or is it even possible that he already sold these stocks long ago and these old pieces of paper were just left in a shoebox? Assuming a share back then is worth a share today, he's looking at about $5k at today's Pepco stock prices. That will pay for a month in the nursing home.