Comments and altering file suddenly not allowed, security property grayed out

I was commenting on a PDF in Acrobat (it has 96 comments on it, so far).  Suddenly, the comments line in the menu became grayed out (it may have happened when I saved the file-I habitually save files), and when I went to security settings, where it says that everything is allowed, but the security option is grayed out, as is every other property setting.  I have a clean copy of the file, that can be altered, but I do not want to copy 96 comments to it and 30 bookmarks.  Note that the problem is local to this file.  What do I do?  I have tried reopening the file, using SaveAs to a different name, reopening Acrobat.  I haven't tried restarting my computer.