<Section xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
    <Paragraph>This is a test.</Paragraph>
</Section>

Namespace Converters
 
    <ValueConversion(GetType(Object), GetType(FlowDocument))> Public Class FlowDocumentConverter
        Implements IValueConverter
 
        Public Function Convert(ByVal objValue As Object, ByVal tTarget As Type, ByVal objParam As Object, _
                    ByVal ciCulture As CultureInfo) As Object Implements IValueConverter.Convert
            Using msDocument As New MemoryStream((New ASCIIEncoding).GetBytes(CStr(objValue)))
                Dim fdDocument As New FlowDocument()
                Dim trDocument As New TextRange(fdDocument.ContentStart, fdDocument.ContentEnd)
                trDocument.Load(msDocument, DataFormats.Xaml)
                trDocument = Nothing
                Return fdDocument
            End Using
        End Function
 
        Public Function ConvertBack(ByVal objValue As Object, ByVal tTarget As Type, ByVal objParam As Object, _
                    ByVal ciCulture As CultureInfo) As Object Implements IValueConverter.ConvertBack
            Return Nothing 'Not interested in converting back from a FlowDocument to a String
        End Function
 
    End Class
 
End Namespace

<Page ... xmlns:converters="clr-namespace:Converters" ... >

<Page.Resources>
    <converter:FlowDocumentConverter x:Key="FlowDocumentConverter" />
</Page.Resources>

<FlowDocumentScrollViewer Document="{Binding PropertyName, Converter={StaticResource FlowDocumentConverter}}" />