You cannot do this with Reader. You need the commercial version of Adobe Acrobat or you can use acrobat.com to make a limited number of pdf files.
You can also use Google to search for such a conversion tool; there are plenty of free downloadable or online tools available.
I recall there was a plugin for Office 2k7 that you could get straight from MickeySoft's site whcih would enable you to "Save As PDF".
Pretty sure you need to run the Genuine Advantage tool to make sure you're legal.