Add extension only to QuarkXpress files

Hello,

I have a bunch of data came from am old Windows share. Among them, there are several Quark documents, which even though they show as “QuarkXPress Print Document” or “QuarkXPress Project File”, they do not have an icon assigned if they don’t have the proper extension.

How can I find all the document based on their type and add the missing extension?

Regards

Kostas