A primary Key cannot contain duplicates, as far as I know. So yes, its quite likely that some combination of of keys sets a primary key.
I am not familiar with Access 2007, and if I recalll correctly, thats what you were working in. There should however still be a button in hte ribbon called "indexes". In 2003 its icon is a few lines of text on the left and some lightning on the right. Click it, and you can see an overview of the indexes in the table, and also which are set as primary key (or if a combination is set as primary key)