PDF e-mail attachments won't open in Reader automatically

I'm stumped, maybe somebody can help. A user starts composing an e-mail through Goldmine, attaches a PDF, then tries to open the PDF from the e-mail (before she sends it) by double-clicking. The message comes up, asking her to choose a program to use, she chooses Reader and it opens, but the "always use this program..." setting doesn't stick. File types are configured properly in Windows, and she can double-click a PDF anywhere else on her computer and it opens normally. If she attaches a Word doc the same way and tries to open it from the e-mail, it will open in Word automatically. The only attachments with a problem are PDFs. We'd like to eliminate the step where she has to choose Reader to open the file every time she does this. She is using Reader 7. Other users with the same image/configuration are able to do this properly. Any advice?