As Josef said, if it's OpenXML (Office 2007) document you can use the managed .net classes to easily update the document, which is basically modifying a bunch of xml files, zipped and renamed to .docx . Visual Studio tools for Office (VSTO) should help you out if need be for Office 2000 and 2003. For previous versions of office you'd need to use Office Automation COM Classes..
Now for updating fields in the word document, you'd need to identify where to insert text to. So if you have some bookmarks or markers to identify the places where you'd like to insert text... you can seek to that position and insert text.
Printing the word doc should be simple since Word has printing support built in. Should be as easy as calling the right method.