There are two possible philosophies for Reader Extensions:
1) That it is a scheme to limit the the actions that one can take on a PDF; think of this as a sort of a security profile operation
2) To provide PDF-based access to capabilities on the PDF without having to buy the full Acrobat Standard/Pro.
Reader Extensions is much more model 2 than model 1. The goal is to allow people to save filled-in forms, sign pdf or comment on the pdf without having to have the full Acrobat std/pro licensed for their desktop. So two other things derive from this:
a) That people who have the full Acrobat version should be able to do anything to the file that they desire
b) But also that they should be aware of actions that they might take on the PDF that would change the file so substantially that it would lose its rights and the ability of downstream Reader users to act on the file.
This (2, and then a and b) is the basic philosophy of Reader Extensions and Acrobat.