I want to create a plugin for Adobe Reader to add extra functionality to the web and mobile PDF reader. How do I approach the subject?

I read the official Adobe documentation but I got confused about the licensing process. If someone can explain it to me, it would be much appreciated.

I tried reading the official site, but there is apparently a free SDK. However, you do need some special limited license to create the plugin, yet there is no explanation as to how to get it.