Just Google that dead link of DocFrac, it gives you the open source location on SourceForge and a download location at SoftPedia.
Seems pretty stable, but haven't tried it myself.
EDIT: It uses a COM DLL, or unmanaged DLL, so to speak. You can link that with ordinary P/Invoke calls, but if you have trouble setting it up, have a look at this post which shows how to do this for converting RTF to HTML with DoxLib. The DLLs are found in the *.gz file from SourceForge. There's even a VB6 example project, but that can only be run with a non-.NET version of VB.