Google is your friend: Be nice and visit him often. He can answer questions a lot more quickly than posting them here...
A very quick search using your subject as the search term
gave nearly one and a half million hits: convert doc to pdf using c - Google Search
Near teh top of the list is a link to an identical question here: Convert word document to pdf without using interop dll.
], but nearly every other link on that page will give you some information...
In future, please try to do at least basic research yourself, and not waste your time or ours.