This can represent a very dangerous situation.He needs to have a swallow evaluation. He may be swallowing poorly, resulting in food entering the breathing passages instead of the passages leading to the stomach. This is "aspiration" and aspiration pneumonia can be the deadly result when food and fluid go into the lungs rather than the stomach. Call the doctor today or go to your local ER. Meanwhile puree diet only, unless that also causes coughing, choking and vomiting. Sorry but this is basically a medical emergency. Call the doctor today.
Sounds like your dad needs to get the doctor ASAP. Something is obviously wrong with him and he needs to be checked out right away. Either an appointment with his PCP is in order, or a trip to the ER.
Good luck!