No I don't think it's only for commercial books.
Actually, have you tried just double-clicking the book? (or whatever the mac equivalent is). It should probably be associated to open with Adobe Digital Editions. Or maybe Adobe Digital Editions doesn't work well with mac systems... Who knows... I'll repeat myself, get calibre
WHSmith books are geographically restricted for Belgium????
I thought that at least within Europe there were no geographical restrictions... This is getting a bit too much!