Is this a possible way of getting free food from McDonald’s?

No. Others had that idea decades ago and Maccy D quickly learned not to be fooled again by that trick.

And you don’t know the difference between the words “free” and “theft”. 

Whether you could do this and get away with it, or not, you should be ashamed of even considering it. Its THEFT.  How much is a burger there, anyhow, pay the damn price and become a decent and honest person. 

in psychology its termed for such a BEHAVIOR  is "GAS LIGHTING " it works on some people POSSIBILITY a thing or action that  CAN happen or be the case the STATE or FACT  of being likely     a thing or action  that may be CHOSEN or DONE  out of SEVERAL  ALTERNATIVES... such a action a person could be charged with FRAUD.. FRAUD  wrongful or criminal  intended  DECEPTION  to result in financial or  personal gain  the INTENTIONAL PERVERSION of the TRUTH  in order  to INDUCE  another to part with something of value  or surrender a legal right

You. You, sir, are a Genus.

You'd be caught because each vehicle pops a separate receipt and a separate order. This won't work, and you could be arrested for fraud or theft.

No.  They actually have a way to mark multiple orders to the same vehicle.  Most locations will allow you to make two separate orders per vehicle in case two different people are in the car and want to pay separately.  Could you get away with it once?  Maybe if you had a new employee but like most things, greed will get the best of you and you'll eventually get caught.  99% of locations have cameras in their drive thru so they'll have your plates and can report you to the popos. 

you get an order number. you cannot have 2 order numbers. they will think you're a dumba*s

no wait to they close up, the left overs goes out in trash

Wait until they close then raid the dumpsters.:)

Yes, if you don't have a receipt for both orders.

It would come up on their screen that your vehicle has 1 specific order. If your vehicle had 2 orders within the same vehicle then it would show up only still as one order.

No, they would realize it was for a different car.  You would still have to pay.