C# – saving a FlowDocument to disk as an XPS document

yes, make a copy of the FlowDocument before printing it. This is because the pagination and margins will be different. This works for me.

    private void DoThePrint(System.Windows.Documents.FlowDocument document)
    {
        // Clone the source document's content into a new FlowDocument.
        // This is because the pagination for the printer needs to be
        // done differently than the pagination for the displayed page.
        // We print the copy, rather that the original FlowDocument.
        System.IO.MemoryStream s = new System.IO.MemoryStream();
        TextRange source = new TextRange(document.ContentStart, document.ContentEnd);
        source.Save(s, DataFormats.Xaml);
        FlowDocument copy = new FlowDocument();
        TextRange dest = new TextRange(copy.ContentStart, copy.ContentEnd);
        dest.Load(s, DataFormats.Xaml);

        // Create a XpsDocumentWriter object, implicitly opening a Windows common print dialog,
        // and allowing the user to select a printer.

        // get information about the dimensions of the seleted printer+media.
        System.Printing.PrintDocumentImageableArea ia = null;
        System.Windows.Xps.XpsDocumentWriter docWriter = System.Printing.PrintQueue.CreateXpsDocumentWriter(ref ia);

        if (docWriter != null && ia != null)
        {
            DocumentPaginator paginator = ((IDocumentPaginatorSource)copy).DocumentPaginator;

            // Change the PageSize and PagePadding for the document to match the CanvasSize for the printer device.
            paginator.PageSize = new Size(ia.MediaSizeWidth, ia.MediaSizeHeight);
            Thickness t = new Thickness(72);  // copy.PagePadding;
            copy.PagePadding = new Thickness(
                             Math.Max(ia.OriginWidth, t.Left),
                               Math.Max(ia.OriginHeight, t.Top),
                               Math.Max(ia.MediaSizeWidth - (ia.OriginWidth + ia.ExtentWidth), t.Right),
                               Math.Max(ia.MediaSizeHeight - (ia.OriginHeight + ia.ExtentHeight), t.Bottom));

            copy.ColumnWidth = double.PositiveInfinity;
            //copy.PageWidth = 528; // allow the page to be the natural with of the output device

            // Send content to the printer.
            docWriter.Write(paginator);
        }

    }

You should not persist the FlowDocument directly as it should be considered the runtime representation of the document, not the actual document content. Instead, use the TextRange class to Save and Load to various formats including Rtf.

A quick sample on how to create a selection and save to a stream:

var content = new TextRange(doc.ContentStart, doc.ContentEnd);

if (content.CanSave(DataFormats.Rtf))
{
    using (var stream = new MemoryStream())
    {
        content.Save(stream, DataFormats.Rtf);
    }
}

To load content into a selection would be similar:

var content = new TextRange(doc.ContentStart, doc.ContentEnd);

if (content.CanLoad(DataFormats.Rtf))
{
    content.Load(stream, DataFormats.Rtf);
}