the encryption algorithm used by Acrobat 9 has ben found to be less secure
than the algorithm used by Acrobat 7, so as of 2.11.19 a request for Acrobat 9 encryption
will fall back to Acrobat 7 encryption.
DocumentPanel.redraw() is no longer required as this object now listens to
PropertyChangeEvents fired by the PDF. This method is not called
anywhere and is a no-op