Is carpet installation easier before or after installation of doors?
I'll assume you're installing a door and jamb, if you aren't installing a jamb I'd hold off on the door until the carpet is installed so it's not in the way

If you're installing the jamb I would do it before the carpet so the jamb can rest on the ground. If it has a threshold you'll have to install it before the carpet. I'd remove the door from the jamb and set it aside until the carpet is finished.