PDFNet converts MS Office files either via a) Interop or b) via its virtual printer driver.
Because you do not have MS Office on your system, PDFNet will use (b) - virtual printer driver.
Now this works for DOCX on and Server 2008 out of the box, because even since Windows Vista was released WordPad includes capability to view/print DOCX files.
So, if Office is not present, PDFNet simply sends a Printto verb (
http://social.msdn.microsoft.com/forums/en-US/csharpgeneral/thread/987b3ff2-879b-4b44-bd38-17598de5f549 ). A default app handler for the given file extension prints the file to PDFTron PDF Virtual printer - which then saves the result to PDF.
So default Windows system comes with built-in DOCX print capability. If you need to support older DOC formant, or other non-office document you need to install an app that can print the extension and associate it with the printto verb.
I think that MS may offer free office viewers, but there are third party options (www_officeviewers_com ?). For more info see https://groups.google.com/d/msg/pdfnet-sdk/vs2TznaDQhw/jlK3ZUIqD7UJ