Unable to convert file, too many attempts.

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

I have installed the apps to open .doc files. And can right click the file and hit print.
The PDFTron print driver runs (not sure if it saves the pdf somewhere?).
But when calling from my windows service. I still have the same problem as described above.
Is there anything else I am missing?

Is the Convert sample running fine but you have issue with the Windows service? In this case there may be permission issue. You may also need to set-up user impersonation feature. For more info please see: