var dropDownLists = radRichTextBox.Document.EnumerateChildrenOfType<SdtRangeStart>()
     .Where(x => x.SdtProperties is ComboBoxProperties)
     .Select(x => x.SdtProperties).OfType<ComboBoxProperties>();
 var defaultItemString = LocalizationManager.GetString("Documents_ContentControlsGenerator_ListItem");
 foreach (var item in dropDownLists)
 {
     if (item.Items.Count > 0 && item.Items.Any(x => x.Value != defaultItemString) && item.Items.Any(x => x.Value == defaultItemString))
     {
         var occurrence = item.Items.FirstOrDefault(x => x.Value == defaultItemString);
         while (occurrence != null)
         {
             item.Items.Remove(occurrence);
             occurrence = item.Items.FirstOrDefault(x => x.Value == defaultItemString);
         }
     }
 }

System.ArgumentException: 'Requested distance is outside the content of the associated document.'PresentationFramework.dll!System.Windows.Documents.TextPointer.TextPointer(System.Windows.Documents.TextContainer textContainer, int offset, System.Windows.Documents.LogicalDirection direction)
  PresentationFramework.dll!System.Windows.Documents.TextContainer.CreatePointerAtOffset(int offset, System.Windows.Documents.LogicalDirection direction) 
  PresentationFramework.dll!System.Windows.Documents.TextParentUndoUnit.Do() 
  PresentationFramework.dll!MS.Internal.Documents.UndoManager.Redo(int count) 
  PresentationFramework.dll!System.Windows.Documents.TextStore.RedoQuietly(int count)  PresentationFramework.dll!System.Windows.Documents.TextStore.SetFinalDocumentState(MS.Internal.Documents.UndoManager undoManager, System.Collections.Stack imeChangeStack, int appChangeCount, int imeSelectionAnchorOffset, int imeSelectionMovingOffset, int appSelectionAnchorOffset, int appSelectionMovingOffset)  PresentationFramework.dll!System.Windows.Documents.TextStore.HandleCompositionEvents(int previousUndoCount)  PresentationFramework.dll!System.Windows.Documents.TextStore.GrantLockWorker(MS.Win32.UnsafeNativeMethods.LockFlags flags)   PresentationFramework.dll!System.Windows.Documents.TextStore.RequestLock(MS.Win32.UnsafeNativeMethods.LockFlags flags, out int hrSession)

FormatException: The input string '4514.5' was not in the correct format.
at System.Single.Parse(String s)
Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.TableImporter.ImportTableGrid(Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Parsing.Style style)  Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.TableImporter.Import(Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Parsing.Style parentStyle)  Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.MainDocumentImporter.BuildTable(Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Parsing.Style parentStyle)  Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.MainDocumentImporter.BuildBody()  Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.MainDocumentImporter.BuildDocument()  Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.MainDocumentImporter.Import()Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.DocxImporter.ReadXmlContentFromPackage(Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.DocxPartImporterBase importer)  Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.DocxImporter.ReadXmlContentAndRelationsFromPackage(Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.DocxPartImporterBase importer)
Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.Import.DocxImporter.Import()  Telerik.Windows.Controls.RichTextBox.dll!Telerik.Windows.Documents.FormatProviders.OpenXml.Docx.DocxFormatProvider.Import(System.IO.Stream input) 

 var cultureCache = Thread.CurrentThread.CurrentCulture;
 Thread.CurrentThread.CurrentCulture = System.Globalization.CultureInfo.InvariantCulture;
 Thread.CurrentThread.CurrentUICulture = System.Globalization.CultureInfo.InvariantCulture;
 var provider= new DocxFormatProvider();
 rtb.Document = provider.Import(stream);
 Thread.CurrentThread.CurrentCulture = cultureCache;
 Thread.CurrentThread.CurrentUICulture = cultureCache;

static MainWindow()
{
    EventManager.RegisterClassHandler(typeof(RadMenuItem), PreviewMouseLeftButtonUpEvent, new MouseButtonEventHandler(OnRadMenuItemPreviewMouseLeftButtonUp), true);
}

private static void OnRadMenuItemPreviewMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
    RadMenuItem radMenuItem = (RadMenuItem)sender;

    RadContextMenu radContextMenu = radMenuItem.ParentOfType<RadContextMenu>();

    if (radContextMenu != null)
    {
        PropertyInfo menuPropertyInfo = radMenuItem.GetType().GetProperty("Menu", BindingFlags.Public | BindingFlags.Instance);
        if (menuPropertyInfo != null)
        {
            MethodInfo setMethod = menuPropertyInfo.GetSetMethod(true);
            if (setMethod != null)
            {
                Application.Current.Dispatcher.BeginInvoke(new Action(() =>
                {
                    setMethod.Invoke(radMenuItem, new object[] { radContextMenu });
                }), System.Windows.Threading.DispatcherPriority.Background);
            }
        }
    }
}