I would like to use C # to convert a doc file to a docx file.
Can this be done without Word on the server?
You can use Aspose.Words . It is not free, but it is good.
http://b2xtranslator.sourceforge.net/
I am not sure if this is possible without Word installed.
Look at this:
http://social.msdn.microsoft.com/Forums/en-US/vsto/thread/f51bdd0c-b022-45c6-8af5-6ed79ad576fd/
You can use OpenOffice for conversion. It supports the .doc format. About the docx format I'm not sure.