Percy T

Hi I'm moved to a new Job so here at my new job there's File Maker Pro 8.x but in my old job there was a 5.X version. When I tried to open a file (made in version 5.x at my old job) it asks for a user and password but when I created it only asked me for a password not a user, so I don't know what user it was and only opens it with guest access and I can't modify the layout. Does anyone can give me a clue about this? THANKS