static void Main(string[] args)
        {
            Telerik.WinForms.Documents.Model.RadDocument templateDocument = GetDocument("Template.rtf");
            Telerik.WinForms.Documents.Model.RadDocument contentDocument = GetDocument("Content.rtf");

            Telerik.WinForms.Documents.Model.Merging.InsertDocumentOptions options = new Telerik.WinForms.Documents.Model.Merging.InsertDocumentOptions();
            options.ConflictingStylesResolutionMode = Telerik.WinForms.Documents.Model.Merging.ConflictingStylesResolutionMode.RenameSourceStyle;
            options.InsertLastParagraphMarker = true;

            Telerik.WinForms.Documents.Model.RadDocumentEditor templateEditor = new Telerik.WinForms.Documents.Model.RadDocumentEditor(templateDocument);
            templateEditor.InsertFragment(new Telerik.WinForms.Documents.Model.DocumentFragment(contentDocument));

    
            string mergedDocumentFilePath = "MergeDocumentsWithRichTextEditor.rtf";
            File.Delete(mergedDocumentFilePath);
            WriteDocToFile(templateDocument, mergedDocumentFilePath);

        }
        private static Telerik.WinForms.Documents.Model.RadDocument GetDocument(string rtfFilePath)
        {
            Telerik.WinForms.Documents.Model.RadDocument document = null;
            var rtfImporter = new Telerik.WinForms.Documents.FormatProviders.Rtf.RtfFormatProvider();
            using (Stream stream = File.OpenRead(rtfFilePath))
            {
                document = rtfImporter.Import(stream);
            }
            return document;
        }


        private static void WriteDocToFile(Telerik.WinForms.Documents.Model.RadDocument doc, string filename)
        {
            var rtfExporter = new Telerik.WinForms.Documents.FormatProviders.Rtf.RtfFormatProvider();
            string rtfText = rtfExporter.Export(doc);
            File.WriteAllText(filename, rtfText);

            Process.Start(filename);
        }

************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an object.
   at Telerik.WinControls.RichTextEditor.UI.PasteOptionsPopup.OnRichTextBoxLayoutUpdated(Object sender, EventArgs e)
   at Telerik.WinControls.Layouts.ContextLayoutManager.fireLayoutUpdateEvent()
   at Telerik.WinControls.Layouts.ContextLayoutManager.UpdateLayout()
   at Telerik.WinForms.Documents.UI.DocumentPrintPresenter.Telerik.WinForms.RichTextEditor.IDocumentEditorPresenter.UpdateLayout()
   at Telerik.WinForms.RichTextEditor.RadRichTextBox.<>c__DisplayClass653_0.<UpdateEditorLayout>b__0()
   at Telerik.WinForms.RichTextEditor.RadRichTextBox.UpdateEditorLayout(Boolean focusCarret, Boolean updateCaretSize, Boolean async)
   at Telerik.WinForms.RichTextEditor.RadRichTextBox.set_ActiveEditorPresenter(IDocumentEditorPresenter value)
   at Telerik.WinForms.RichTextEditor.RadRichTextBox.Telerik.WinControls.UI.IPrintable.BeginPrint(RadPrintDocument sender, PrintEventArgs args)
   at Telerik.WinControls.UI.RadPrintDocument.OnBeginPrint(PrintEventArgs e)
   at System.Drawing.Printing.PrintDocument._OnBeginPrint(PrintEventArgs e)
   at System.Drawing.Printing.PrintController.Print(PrintDocument document)
   at System.Drawing.Printing.PrintDocument.Print()
   at System.Windows.Forms.PrintPreviewControl.ComputePreview()
   at System.Windows.Forms.PrintPreviewControl.CalculatePageInfo()
   at System.Windows.Forms.Control.InvokeMarshaledCallbackDo(ThreadMethodEntry tme)
   at System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(Object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Forms.Control.InvokeMarshaledCallback(ThreadMethodEntry tme)
   at System.Windows.Forms.Control.InvokeMarshaledCallbacks()

this.radRichTextEditor1.Text = null;

        private void radButton1_Click(object sender, EventArgs e)
        {
            HyperlinkInfo info = new HyperlinkInfo()
            {
                NavigateUri = "http://www.google.com",
                Target = HyperlinkTargets.Blank,
                IsAnchor = false
            };
            this.radRichTextEditor1.InsertHyperlink(info, "www.google.com");
        }

        private void radButton2_Click(object sender, EventArgs e)
        {
            LightVisualElement button = new LightVisualElement();
            button.Text = "My Button";
            button.DrawFill = true;
            button.BackColor = System.Drawing.Color.Yellow;
            button.GradientStyle = Telerik.WinControls.GradientStyles.Solid;

            Section section = new Section();
            Paragraph paragraph = new Paragraph();
            InlineUIContainer container = new InlineUIContainer();
            RadElementUIContainer radContainer = new RadElementUIContainer(button);
            container.UiElement = radContainer;
            container.Height = 25;
            container.Width = 70;
            paragraph.Inlines.Add(container);
            section.Blocks.Add(paragraph);
            RadDocument doc = new RadDocument();
            doc.Sections.Add(section);
            radRichTextEditor1.InsertFragment(new DocumentFragment(doc));
        }

        private void radButton3_Click(object sender, EventArgs e)
        {
            Telerik.WinForms.Documents.Model.RadDocument document = radRichTextEditor1.Document;

            Telerik.WinForms.Documents.FormatProviders.Html.HtmlFormatProvider provider = new Telerik.WinForms.Documents.FormatProviders.Html.HtmlFormatProvider();

            provider.ExportSettings.InlineUIContainerExporting += ExportSettings_InlineUIContainerExporting;

            provider.ExportSettings.DocumentExportLevel = Telerik.WinForms.Documents.FormatProviders.Html.DocumentExportLevel.Fragment;
            provider.ExportSettings.ExportFontStylesAsTags = true;
            provider.ExportSettings.SpanExportMode = Telerik.WinForms.Documents.FormatProviders.Html.SpanExportMode.DefaultBehavior;
            string htmlValue = provider.Export(document);
            webBrowser1.DocumentText = htmlValue;
        }

        private void ExportSettings_InlineUIContainerExporting(object sender, Telerik.WinForms.Documents.FormatProviders.Html.InlineUIContainerExportingEventArgs e)
        { 
        }

this.radRichTextEditor.Document.Selection.AddDocumentElementToSelection(span);
this.radRichTextEditor.Delete(false);