I have to work with ISO-purchased pdf documents that are heavily DRM-controlled. I can only open them on two PCs with a plugin that only works in Acrobat reader. It is so closed and unusable.
In practice, I don't know why people are talking about PDF. In any recent time, I have only seen people using Adobe readers by accident and haven't heard about anybody using their editor for any reason. I know of some people that buy their editors, just not any that use it.