Yes, you can. It will require an amount of money roughly equal to the original price to be able to do it for any length of time on actual singletrac. The frame geometry is not going to let you be Joe racer boy, but it will work fine for now.
I dunno if I'd convert it, I think I'd try to find some knobby-ish tires for it and work really hard on picking good lines and taking bumps with your arms and legs while saving up for another bike. and perhaps get some ergo grips to soften the bumps. As it is that bike is a pretty good commuter/path bike. if you spent $400 to $500 on converting it to an mtb it would still be worth about $300 or $400 due to the frame/drivetrain etc.. even though you have about $800 or $900 into it. plus it wouldn't be that great on road. But if you spent $500 on an mtb you'd still be out of pocket about $800 or $900 total but you would have a pretty good commuter/comfort bike and a nice beginner/intermediate off road bike.