How to get a FlowDocument from the PrintSettings?

string rtf = editor.Document.CurrentSnapshot.Export(new TextExporterFactory().CreateRtf());
MemoryStream ms = new MemoryStream(Encoding.Default.GetBytes(rtf));

FlowDocument flowDocument = new FlowDocument() { FontSize = editor.FontSize, FontFamily = editor.FontFamily };
TextRange textRange = new TextRange(flowDocument.ContentStart, flowDocument.ContentEnd);
textRange.Load(ms, DataFormats.Rtf);

int index = 0;

Paragraph p = flowDocument.Blocks.FirstBlock as Paragraph;

while (p != null)
{
    p.Inlines.InsertBefore(p.Inlines.FirstInline,
        new Run(string.Format("{0,-5} ", ++index))
        {
            Foreground = editor.LineNumberMarginForeground,
            FontFamily = editor.LineNumberMarginFontFamily,
            FontSize = editor.FontSize - 1,
            BaselineAlignment = BaselineAlignment.Center
        });
    p = p.NextBlock as Paragraph;
}