Outlook 2000 is not supported on Windows 7. There may be workarounds but it is not a supported software.
It would seem you have some kind of add on that is converting word to pdf document by default.
Check your control panel add/remove list to see what you have installed.
You might just need to change your default settings.
As I do not use office 2000 any more I cannot really tell where you would look in office. However look in tools options or similar for features that can be disabled or made non default.
If it is a third party software you have installed then uninstall it.
☺ When everything else fails, read the instructions.