I posted recently about the upcoming Word to FlowDocument converter due out later this month.
I should point out that there are a couple existing tools for creating FlowDocuments.
OpenXML Writer is an opensource text editor for creating WordprocessingML files (.docx). The generated files can be opened and edited in Microsoft(TM) Word 2007 and other softwares that support the OpenXML format.
Among the features supported are text formatting options like bold, italic, underline, font color, font name , font size, paragraph justification, text indentation and bullets+numberings. Basic editing functions like cutting, copying, pasting and spell check are also provided.
This tool allows you to enter XAML and have it converted to HTML, or enter HTML and have it converted to XAML.