No. PDF files don't have reliable lock mechanisms. Only the protection by Open Password can give high grade of protection. The PDF standard password security permissions mechanism is used for that but PDF Explorer does not respect these impositions by default, but now that you refer this subject I suppose that I can add a configuration option to control this behavior and refuse edition of files with permission password set.
I suppose you are talking about the possibility to lock the file in the PDF Explorer environment but if I add that option, users can always edit it using some other application.
