It is likely that the database was created before 2013 but I could open it using Access 2013. I do recall that whenever I opened it, I got a message asking if I wanted to convert it. I always said no because I was advised that it was likely to lose all of the links, possibly it was bad advice. I do not have any files with a .mdw extension. The message I get when I try to open the database with Access for Office 365 is "Cannot open a database created with a previous version of your application".