It is wayyy to complicated to convert a doc to pdf, if you are just wanting to use your own code. I agree with LizR, use a pdf printer. You can use Ghostscript PDF Printer and call through code. I have also used pdf995. The pdf spec is fairly complicated and isn't something that you can just code in a short amount of time.
Yes I know lizR, but anyway, this assembly could be nested to the hole application, or better he could reverse it and try to build his own assembly based on idea found there, may be it will be a suitable solution for him