Restrict editing

Can somebody explain the function of the Restrict editing check box that is automatically selected for documents that have been signed through Adobe Sign.  I noticed this option is automatically checked after a document is sent through Adobe Sign.  While testing the security of a document I tried to uncheck it.  An information window opened stating that "I cannot change security on this document becasue the document is signed or certified".  Perftect and just what I expeced, but after clicking OK another information window opened asking if "are you sure you want to remove security from this document".  This was unexpected because it would invalidate the seucrity of a signed document.  I clicked OK and was prompted to enter a "Permissions Password", which I have no idea who set it and what it was set to.  My concerns are whiy is this option enabled and also that a brute force attack on the Permissions Password could allow the document to be altered after signing.