My understanding is that there is currently no legal requirement to teach a PDC. Also, as far as I know there is no certification body that controls the term PDC or permaculture. But there are a lot of views on this and from what I have seen it sounds like it is helpful if you go through a PDC before trying to teach your own and that the quality of the PDC is likely to be higher in this case. There are groups like
Permaculture Institute of North America that have their own teaching program to prepare people to teach a PDC. I'm not sure how widespread or accepted that program is within the permaculture community.
But... if all someone did was take a PDC and then go out and try to teach I personally would argue that they are not ready to teach unless they had some solid experience under their belt too.
I would recommend that you start with workshops focusing on one or a small number of related permaculture topics. This way you could get more experience with teaching. Then I would see if you could co-teach with someone else who has experience teaching PDCs. This way your first go with teaching a PDC would not be by yourself.
My understanding is that anyone who wants to teach permaculture can teach permaculture - the question is will what they teach be of any real value to their students? I would start small and build from there if you are going to try to teach - my recommendation is don't start with teaching a PDC.