I've updated to the latest iOS version of Adobe Reader that enables form-filling, and imported several work-related forms with some security protections (changing, assembly, extraction). Filling, signing, and commenting are allowed, yet in the app the documents appear as locked and are unfillable. I even tried extending permissions to Adobe Reader users, but this had no effect. When I open one of these forms, a lock icon in the lower right iPad screen corner reveals a message that the document is protected and "some edits may not be allowed." I can fill it out just fine on the desktop computer. Am I missing something? Seems reasonable to expect many fillable forms to be protected by the author, so this shouldn't hinder the ability to fill or sign them.
The current version of the mobile Adobe Reader does not support filling protected forms. This is a feature we're considering for a future release, though it hasn't bubbled to the top in our planning. Thanks for your feedback, it helps us to know what people are experiencing and expecting.