pdf problem

Hi Guys
I used to send docs. to a friend as pdf attachments and all was fine. I now received the following mail from him:

I'm not receiving your email in the same format anymore, seems like in stead
of an attached .pdf file I now receive all the data imbedded into the email.
I recently upgraded to Windows 8 but are still running Outlook 2003 so I'm
not sure why this is happening.

Is the problem on my side, using XP and Firefox?
Please help.
Thanks,
Ken