If correct and this was a document created from the normal.dot template, but the TEXT wasn't there on initial creation (when the new document was displayed), but some time after when they next checked it. Then I don't think word is infected but you/them may have had a virus that can modify documents, which in itself I don't think is too difficult.
However, why they would do it is the question, why change the author further drawing attention, which isn't your usual virus/trojan behaviour. Unless this was accompanied with some sort of warning/threat to do this to all documents, or suggest some anti-spyware program that could prevent this.
If this were more widespread I would think it was a concerted attack but just one document is weird.
If the document was created on the given date, did the properties show when it was last modified, this could indicate when any un/authorised access to the document took place. The other thing to consider is he the only one to have access to the document/folder or are documents shared, etc.
I would ensure your friend has a good firewall to prevent any unauthorised outbound access to the internet, because if it were and attack, why stop at Branding the Page when you can export potentially valuable data.
I'm sorry there isn't anything else I can suggest.