Ok, let me see if I understand you correctly. In your database you have a field called something like File_Attachment. You have created a formula to display the word "Yes" or "No" if there is anything in the File_Attachement field. Now, if there is something in the field you want to display the file name. Is this correct?
What field in your data contains the file name? You just need to add that field to your report.
-Dell