RadDocument radDocument = null;
XamlFormatProvider xamlformatProvider = new XamlFormatProvider();
using (FileStream inputStream = new FileStream("input.xaml", FileMode.Open))
{
    Console.WriteLine("reading input file");
    radDocument = xamlformatProvider.Import(inputStream);
}

var provider = new Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.DocxFormatProvider();
var bytes = provider.Export(radDocument);

var provider2 = new Telerik.Windows.Documents.Flow.FormatProviders.Docx.DocxFormatProvider();
var flowDoc = provider2.Import(bytes);

var provider3 = new Telerik.Windows.Documents.Flow.FormatProviders.Pdf.PdfFormatProvider();

using (Stream output = File.OpenWrite(@"output.pdf"))
{
    Console.WriteLine("writing output file");
    provider3.Export(flowDoc, output);
}

Console.WriteLine("done...");
Console.ReadKey();

  this.radRichTextBox.PreviewEditorKeyDown += (sender, args) =>
     {
         if (Keyboard.Modifiers.HasFlag(ModifierKeys.Alt) && Keyboard.Modifiers.HasFlag(ModifierKeys.Control) && args.Key == Key.E)
         {
             args.SuppressDefaultAction = true;
             args.OriginalArgs.Handled = true;
             this.radRichTextBox.Insert("€");
         }
     };

RadDocument radDocument1 = RtfSourceProvider.Import(rtf1);
RadDocument radDocument2 = RtfSourceProvider.Import(rtf2);

AppendDocumentOptions options = new AppendDocumentOptions();
options.FirstSourceSectionPropertiesResolutionMode = SectionPropertiesResolutionMode.NoSectionBreak;

RadDocumentMerger merger = new RadDocumentMerger(radDocument1);
merger.AppendDocument(radDocument2, options);

RichText.Document = merger.Document;

 StyleManager.ApplicationTheme = new Office2016Theme();

  public class MyRenderer : SpreadStreamExportRenderer
  {
      public override void SetCellValue(DataType dataType, object value)
      {
          DateTime date;
          if (value != null && DateTime.TryParse(value.ToString(), out date))
          {
              base.SetCellValue(DataType.DateTime, date);
              var cell = this.GetCell() as ICellExporter;
              cell.SetFormat(new SpreadCellFormat() { NumberFormat = "yyyy-MM-dd HH:mm:ss" });
              return;
          }
          base.SetCellValue(dataType, value);
      }
  }

 spreadStreamExport.RunExportAsync(FILENAME, new MyRenderer(), options);