Generally, they are pneumatic (running on compressed air).
You can hear the compressors humming away when the brake is released, or after the doors have been cycled.
There is a pressure guage on some trains, look for it on the ends of the bench seats, by the doors.
If they are a linear push mechanism or a form of pneumatics, they would be difficult to move unassisted (without the mechanism operating) if you could move them at all.
The same can be some for most coach, bus and train doors.