We do not use MS FlowDocument internally. As you may know FlowDocument is actually not available in Silverlight 4. We have our own model for our flow documents (the same for Silverlight and WPF), which resembles the document structure of the MS FlowDocument. It includes similar document elements - Section, Paragraph, Table, TableRow, TableCell, Span, ImageInline and InlineUIContainer, but they are implemented from scratch and do not use the elements defined in the System.Windows.Documents assembly.
We are also working on a couple of FormatProviders that can convert documents from telerik Document to WPF FlowDocument/Silverlight RichTextBox documents and vice versa. They should be ready for 2011.Q1 version, where also RadRichTextBox for WPF will be introduced for the first time.
If you have any other questions, do not hesitate to contact us again.
All the best,
the Telerik team
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