I have a 2015 F250 diesel. Bought new and has 35,000 miles on it. You can see I don't drive it much as I am retired. I was wondering if it is a good thing to put diesel fuel additive in it since I only do short trips.

 

There are some additives that help rid the tank and fuel lines of a little bit of water, provide additional lubrication to fuel components,
lower the point where the fuel can gel and cause difficult operation in freezing weather
and some that claim to clean injectors. You might check out a truck stop and see what they have and make your decision once you see what is available.
If possible , try to have the engine run at operating temp as much as possible to prevent problems caused by the engine not running at operating temps.
Have you checked your owner's manual?