Blow the film with electric hair drier.
Wipe it off using cloth with some water.
Now that it is hard and crisp, it can be removed with some solvents. You can also buy some products which are similar to glue cleaner of WD-40 or 3M glue. Spray the glue cleaner on the protective film and wait for ten minutes or so. And then it will be easier to remove the protective film.
Drop some Huaren multifunctional glue cleaner on the door and tear the film off 20 seconds later.
