It's often annoying to wait for Norton's antivirus scanner to complete when you open a document - it's also a waste of your time if you have it set on 'autoprotect' as that causes it to scan every write to the drive and even documents opened right from an email are written to the drive before opening.

In recent versions of Norton Antivirus: Open the Options dialog and click on Miscellaneous. Remove the check from the Office plug-in option. (Older versions require a registry edit.)