How do I move a PDF picture from an email on my iPad to my pictures?

You can't save a PDF directly to the photos app, but if you can open the PDF in the mail app and get the entire PDF to appear on the screen, take a screenshot of it and that will be saved to the photos app camera roll.

Hold down on the sleep button and the home button at the same time briefly until you see the white flash on the screen and hear the shutter sound. That's how to take a screenshot.

You should probably tap and hold down on the PDF in the mail app and select it to open in iBooks or another PDF app that you might have on the iPad.