Put it in a box on the particular slide. If you plan to talk them thru it, just start with the cover then say
"Ok, I'd like to walk you thru my portfolio - if you'll just open it up the pdf we'll start on page 1. Please let me know if you have any questions. You got the pdf open? Great! *start talking*"
You don't have to control the 'playback' of what they are seeing. Just tell them when you're going to a new page.