Link over phrase which results in a pop up

Hello,

I'm hoping someone will be willing to help me. In a pdf file, I would like to create a link over words and phrases which when clicked results in a simple pop up with some extra information which I would add. I've seen that you can hover over a word to get a pop up, but I'm hoping to be able to only see it when you click on the word or expression.

I have a rather old version of adobe: 8.3.1. I should also say that I'm a beginner when it comes to editing pdf documents.

Any advice would be greatly appreciated. Thanks in advance.