Maybe use the browser object to load the pdf in the same way as a webpage with the go to URL action? I don't recall what it's called, but you should find it in the list. It will either cause the off to download or maybe in the case of chrome it may let you view it there.
Another way would be to use a pdf js library. It's hard because of all the hoops you have to jump through to get it to display in a c2 game. Probably nigh impossible if that didn't make sense.
The final option, although you should check here first, is to see if a pdf plugin exists already that you can use. There in a topic in the addons section that lists all third party plugin's. I'm too lazy to check myself.