A good easy home remedy to keep your car doors from freezing shut in the winter is to use some Pam cooking spray or any other cooking spray lubricant.
Spray the seals on both the door and the frame where the door closes with the Pam or other cooking spray and then it will keep the door from sticking.
The Pam cooking spray also keeps the doors seals lubricated as well and protects then.
You can also spray some WD40 on the doors seals and around the door to help displace water which will prevent ice from building up on the doors seals and then the door should open.
You can also use a hair dryer to melt the ice around a car door and car door lock to get it open when the ice has frozen it shut.
Spray the door locks with some WD40 as well to not only lubricate it but also keep water out of it so that the lock doesn't freeze.
They make and sell some car lock de icer as well.