Perhaps I misunderstood, but I thought you said you already implemented that functionality…

they are able to view the details of the order in a pop up that looks like a purchase order.

 
 

Oh, ok. You didn’t mention PDF in your initial post. You could also capture an image of the order that you’re already displaying in the popup, but that would require a plugin as well. It would be a raster image, though, so PDF might be a better option.