«Document .Net» will help you in development of applications which operates with DOCX, RTF, PDF and Text documents. After adding of the reference to "SautinSoft.Document.dll" (it's 100% C# managed assembly) you will be able to create a new document, parse an existing, modify anything what you want. Not too shabby! Let us say:

Generate new document on fly and fill it by necessary data.
Load existing document and get all it's structure as tree of objects.
Modify paragraph formatting, text, tables, TOC and other elements in existing document.
Parse the document and get the tree of its objects.
Replace, merge any data in documents and save as new DOCX, Text or RTF.
Convert between PDF, DOCX, RTF and Text.