This should come as no surprise to anyone in the consulting, marketing, or PR fields. You always send PDF documents for this very reason.
Word XP has an option on the Tools|Options|Security tab titled: Remove personal information from file properties on save. It’s always a good idea to have this checked. Details on the kind of metadata available in Word documents and removal instructions are detailed in the Microsoft Knowledge Base.
The moral of the story: Use the PDF format for external communications.