OK, some missinformation here, needs clarification.
That means they can land next to a city and attack in the same turn.
No, they can’t
I believe if they have the commando promotion they can attack after paradropping.
No, commando or not, no attack after drop.
Yeah, they can't attack in the same turn but they can para-drop from any city/fort they're in - even if it's just an Open Borders agreement.
Not correct.
You can paradrop from your and your vassal’s cities and also from forts that are within your own territory or your vassal.
You can paradrop from cities you have open borders
but you can’t paradrop from forts which are within regions you have open borders with.
What they can do after the drop:
-> Move: normally 1 tile, commando promotion gives you 2 tiles on enemy roads
and 5 tiles on enemy rails after drop
-> Pillage
My paras usually have 4 tasks:
-> Pillage important ressource (like oil) on first war-turn
-> stack defender for tank SoD (usually Guerilla-II on hill tiles)
-> capturing poor defended cities in the “outback” (far away from the enemy core, not worth sending the main stacks)
-> Woodsman-III / Medic-I healer units, built from red-cross city to keep up with fast tank SoD (no need to use great generals for Medic-III units, has the same healing rate)