The real answer is that there's nothing to "fix"- the device is working
as it's supposed to. The ".att" files are supposed to be opened in the
email itself by tapping on the file name; you aren't supposed to sneak in
the back door! ;)
To open the file in PWord anytime you like, simply tap and hold on the
attachment's file name in the email then select "save as." This will
allow you to save the attachment on the device just like you would save
an atachment to your desktop in desktop Outlook, and then you can access
it directly in PWord even after you delete the email.