<Style TargetType="telerik:RadVirtualKeyboardWindow">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="telerik:RadVirtualKeyboardWindow">
                <Grid>
                    <!-- Fensterinhalt -->
                    <Border Background="{TemplateBinding Background}">
                        <ContentPresenter />
                    </Border>

                    <!-- Schließen-Button -->
                    <Button x:Name="PART_CloseButton"
                            Width="24" Height="24"
                            HorizontalAlignment="Right"
                            VerticalAlignment="Top"
                            Margin="5"
                            Background="DarkRed"
                            Foreground="White"
                            BorderBrush="Transparent"
                            Content="✕"
                            FontWeight="Bold"
                            Cursor="Hand"/>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

       public static void Print(List<string> files)
       {
           using (MemoryStream stream = new MemoryStream())
           {
               using (PdfStreamWriter fileWriter = new PdfStreamWriter(stream, leaveStreamOpen: true))
               {
                   foreach (string path in files)
                   {
                       using (PdfFileSource fileSource = new PdfFileSource(new MemoryStream(File.ReadAllBytes(path))))
                       {
                           for (int i = 0; i < fileSource.Pages.Length; i++)
                           {
                               PdfPageSource sourcePage = fileSource.Pages[i];
                               using (PdfPageStreamWriter resultPage = fileWriter.BeginPage(sourcePage.Size))
                               {
                                   // set content                      
                                   resultPage.WriteContent(sourcePage);
                               }
                           }
                       }
                   }
               }

               var pdfViewer = new RadPdfViewer();
               PdfFormatProvider provider = new PdfFormatProvider();
               RadFixedDocument document = provider.Import(stream);
               pdfViewer.Document = document;
               var printdlg = new PrintDialog();
               printdlg.UserPageRangeEnabled = true;
               printdlg.SelectedPagesEnabled = true;
               if (printdlg.ShowDialog() == true)
               {
                   var printSettings = new PrintSettings(Path.GetFileNameWithoutExtension("file"), false);
                   pdfViewer.Print(printdlg, printSettings);
               }
           }
       }

                            <telerik:RadGridView
                                Margin="0,5,0,0" AutoGenerateColumns="False" BorderThickness="0" BorderBrush="{StaticResource LaGrey12}"
                                ColumnBackground="{StaticResource LaGrey12}"
                                GridLinesVisibility="None" IsReadOnly="True"
                                ItemsSource="{Binding ContactActivityNote.ContactActivityParticipants}"
                                ShowColumnHeaders="False">
                                <telerik:RadGridView.Columns>
                                    <telerik:GridViewDataColumn
                                        Width="Auto"
                                        DataMemberBinding="{Binding ParticipationTypeId}"
                                        Header="Type" />
                                    <telerik:GridViewDataColumn
                                        Width="*"
                                        DataMemberBinding="{Binding AddressedTo}"
                                        Header="Addressed To" />
                                </telerik:RadGridView.Columns>
                            </telerik:RadGridView>

if (e.Key == System.Windows.Input.Key.Tab)
{
    string typedText = MultiColumnComboBox
        .FindChildByType<TextBox>()
        .Text
        .Trim();

    if (MultiColumnComboBox.DropDownContentManager.DropDownElement is RadGridView gridView)
    {
        string keyFieldName = gridView.Columns[0].UniqueName;

        var itemToSelect = gridView.Items
            .OfType<DataRow>()
            .FirstOrDefault(row =>
            {
                var keyValue = row[keyFieldName];
                return keyValue != null &&
                       keyValue.ToString().Equals(typedText, StringComparison.OrdinalIgnoreCase);
            });

        if (itemToSelect != null)
        {
            gridView.SelectedItem = itemToSelect;
        }
    }
}