Create two different passwords, one for each kind of user with access to the document. With one of the passwords, edit the document's information, format, and metadata; and with the other, you can access the document to read it but not edit it. Using this application is as easy as dragging the file that you want to encrypt to the window, choosing the two passwords you want to use, and pressing the 'lock' button. After you've locked the document, you can always unlock it or just delete the password.
Wonderfulshare PDF Project is a very useful, simple, and effective application that will satisfy all your needs in terms of protecting the privacy of your PDFs.