You make an interactive PDF for an iPad the same way you do for a Mac or PC.
However, you may need to "rein in" your expectations about the kind of interactivity that can be included. Probably the most commonly used PDF reader on an iPad is Adobe Reader. However, it cannot handle many kinds of interactivity, including most buttons as well as media (video, sound). Be sure to test your interactive PDF on the readers which you expect your readers to use.
Other (usually paid apps) have better support of interactive PDF. I recommend PDF Expert which costs US $9.99. Try some out when you're planning your project to see what works.
