File attached to message without user knowledge

[Gugy Pen]

One of my users says that a pdf file got attached to an unrelated message he was sending without his attaching it. The pdf file was in his Windows Clipboard, so I think that he probably pressed Ctrl-V by mistake, but he insists not. Besides using the paperclip attachment, right click paste or ctrl-V are there other ways that a file could get attached to an email?

I can't find any reference to spyware that would cause this?

Using Windows XP Pro SP2, Office 2003 SP3.

Thanks!