Не отображается текст в pdf-файле, экспортированного из DataGrid

Подскажите, что не так?

public DataGridCell GetCell(int row, int column)
    {
        DataGridRow rowContainer = GetRow(row);

        if (rowContainer != null)
        {
            DataGridCellsPresenter presenter = GetVisualChild<DataGridCellsPresenter>(rowContainer);

            DataGridCell cell = (DataGridCell)presenter.ItemContainerGenerator.ContainerFromIndex(column);
            if (cell == null)
            {
                dataGrid_postoffices.ScrollIntoView(rowContainer, dataGrid_postoffices.Columns[column]);
                cell = (DataGridCell)presenter.ItemContainerGenerator.ContainerFromIndex(column);
            }
            return cell;
        }
        return null;
    }

    public DataGridRow GetRow(int index)
    {
        DataGridRow row = (DataGridRow)dataGrid_postoffices.ItemContainerGenerator.ContainerFromIndex(index);
        if (row == null)
        {
            dataGrid_postoffices.UpdateLayout();
            dataGrid_postoffices.ScrollIntoView(dataGrid_postoffices.Items[index]);
            row = (DataGridRow)dataGrid_postoffices.ItemContainerGenerator.ContainerFromIndex(index);
        }
        return row;
    }

    public static T GetVisualChild<T>(Visual parent) where T : Visual
    {
        T child = default(T);
        int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
        for (int i = 0; i < numVisuals; i++)
        {
            Visual v = (Visual)VisualTreeHelper.GetChild(parent, i);
            child = v as T;
            if (child == null)
            {
                child = GetVisualChild<T>(v);
            }
            if (child != null)
            {
                break;
            }
        }
        return child;
    }

    private void button_postoffices_exportpdf_Click(object sender, RoutedEventArgs e)
    {
        // Create a new PDF document
        Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 10f, 0f);
        PdfWriter.GetInstance(pdfDoc, new FileStream("PostOffices.pdf", FileMode.Create));
        pdfDoc.Open();

        // Add a table to the PDF document
        PdfPTable pdfTable = new PdfPTable(dataGrid_postoffices.Columns.Count);
        pdfTable.WidthPercentage = 100;

        // Add the column headers to the table
        for (int i = 0; i < dataGrid_postoffices.Columns.Count; i++)
        {
            PdfPCell cell = new PdfPCell(new Phrase(dataGrid_postoffices.Columns[i].Header.ToString()));
            pdfTable.AddCell(cell);
            /*new Phrase(dataGrid_postoffices.Columns[i].Header.ToString())*/
        }

        

        // Copy the data from the DataGrid to the worksheet
        for (int i = 0; i < dataGrid_postoffices.Items.Count; i++)
        {
            for (int j = 0; j < dataGrid_postoffices.Columns.Count; j++)
            {
                //var textData = GetCell(i, j);
                //TextBlock tb = textData.Content as TextBlock;
                //var value = tb.Text;

                pdfTable.AddCell(new Phrase((dataGrid_postoffices.Columns[j].GetCellContent(dataGrid_postoffices.Items[i]) as TextBlock)?.Text ?? ""));
                
                //pdfTable.AddCell(new Phrase(dataGrid_postoffices.Items[i].ToString()));
            }
        }

        // Add the table to the PDF document
        pdfDoc.Add(pdfTable);

        // Close the PDF document
        pdfDoc.Close();
    }