How to Convert Excel XLSX to CSV Files in a WPF App using C#

public partial class MainWindow : Window
{
    public static RoutedUICommand OpenXlsxCommand = new RoutedUICommand(
        "Open XLSX", "OpenXlsx", typeof(MainWindow));
    public static RoutedUICommand SaveCsvCommand = new RoutedUICommand(
        "Save CSV", "SaveCsv", typeof(MainWindow));
    public MainWindow()
    {
        InitializeComponent();
        // Bind Command to Menu Items
        CommandBindings.Add(new CommandBinding(OpenXlsxCommand, OpenXlsxExecuted));
        CommandBindings.Add(new CommandBinding(SaveCsvCommand, SaveCsvExecuted));
    }
    private void OpenXlsxExecuted(object sender, ExecutedRoutedEventArgs e)
    {
        // Load an Existing XSX File
    }
    private void SaveCsvExecuted(object sender, ExecutedRoutedEventArgs e)
    {
        // Export Instace to CSV
    }
}

<DockPanel>
    <Menu DockPanel.Dock="Top">
        <MenuItem Header="_File">
            <MenuItem Header="_Open XLSX" Command="{x:Static local:MainWindow.OpenXlsxCommand}"></MenuItem>
            <MenuItem Header="_Save CSV" Command="{x:Static local:MainWindow.SaveCsvCommand}"></MenuItem>
        </MenuItem>
    </Menu>
</DockPanel>

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="30"/>
        <RowDefinition/>
        <RowDefinition Height="350"/>
        <RowDefinition/>
    </Grid.RowDefinitions>
</Grid>

 <gss:GcFormulaBar x:Name="formulaBar1" Grid.Row="0" ShowEditingButtons="True" Expandable="True"  AssociatedSpread="{x:Reference Name=spreadSheet1}"/>
 <gss:GcSpreadSheet x:Name="spreadSheet1" Grid.Row="1" Grid.RowSpan="3"/>

private void OpenXlsxExecuted(object sender, ExecutedRoutedEventArgs e)
    {
        // Load an Existing XSX File
        Microsoft.Win32.OpenFileDialog ofd = new Microsoft.Win32.OpenFileDialog();
        ofd.DefaultExt = ".xlsx";
        ofd.Filter = "Excel Documents (*.xlsx)|*.xlsx";
        var sel = ofd.ShowDialog();
        if (sel == true)
        {
            // one line of code to import the Excel file into Spread.NET 
            spreadSheet1.OpenExcel(ofd.FileName);
        }
   }

private void SaveCsvExecuted(object sender, ExecutedRoutedEventArgs e)
{
    // Export WPF Instace to CSV
    Microsoft.Win32.SaveFileDialog sfd = new Microsoft.Win32.SaveFileDialog();
    sfd.FileName = "SPNET_XLSX_to_CSV.csv";
    sfd.Filter = "Excel Documents (*.csv)|*.csv";
    sfd.DefaultExt = ".csv";
    var sel = sfd.ShowDialog();
    if (sel == true)
    {
        spreadSheet1.Workbook.SaveAs(sfd.FileName, GrapeCity.Spreadsheet.IO.FileFormat.CSV);
    }
}