I just tried it. Even saved a document with Reader Extended PDF and a signature field (which you can only do with Acrobat). I opened in Reader but could not certify it (although I could digitally sign in). I can certify in Acrobat.
It's possible you can certify a Portfolio (container for PDF docs) using Reader. However, right now that's not working with the current version of Acrobat or Reader. (Adobe engineering is working on that - see my recent posting).
It's also possible that the bug with certifying/signing Portfolios is also preventing other actions from happening. I don't know.
Certification is Acrobat-only feature. You cannot certify in Reader. You can certify in Acrobat only. Some features you cannot get for free. Certification is one of them.
BTW, you can sign in Reader 11.0.7 even if it is not Reader-Extended for signing.