A quick and easy way to convert Microsoft Word (.doc, .docx) files to pdf is to install the free 2007 Microsoft Office Add-in: Microsoft Save as PDF. It is not necessary to close Word or restart it for the add-in to take effect. When finished installed, click Save As… > .pdf to save the file as pdf.
For that matter, this method works for all Office apps including Powerpoint, OneNote, Excel, and others. This is an alternative to buying Adobe Acrobat Pro.