You need to remove both the inner door card and the outer door panel.
Smart 450 door handle removal.
Getting the door panel off and back on take a bit of time and you only need some torx screwdrivers.
Remove the door latching mechanism by removing the 3 torx bolts.
How to remove the door skin of the smart fortwo with ease.
The interior door panel of a smart car.
450 door panel removal.
For the most part shot in real time.
Removing a smart door panel easily quickly and without breaking things.
Small edit while i struggled with the side mirror.