Convert Microsoft Office Document (Word) to PDF using C# and VB.Net in ASP.Net

I am getting an error "This method or property is not available because a document window is not active."  for the line application.Documents.Close(ref missing, ref missing, ref missing);

I have got an another question, /pt cmd can be used to print an office file through command prompt wright ?? I was thinking , can I create a process through asp such that it starts the command prompt with an argument to print a file, where I can make that printer only to convert the file to pdf ?? Can I do that ?? any suggestions . .