在使用iText在C#中添加頁眉和頁腳時，可以使用PdfPageEventHelper類來實現。以下是一個簡單的示例代碼：

using iTextSharp.text;
using iTextSharp.text.pdf;

public class HeaderFooter : PdfPageEventHelper
{
    public override void OnEndPage(PdfWriter writer, Document document)
    {
        base.OnEndPage(writer, document);

        PdfPTable header = new PdfPTable(1);
        header.TotalWidth = document.PageSize.Width - document.LeftMargin - document.RightMargin;
        header.DefaultCell.Border = Rectangle.NO_BORDER;

        PdfPCell cell = new PdfPCell(new Phrase("Header"));
        cell.HorizontalAlignment = Element.ALIGN_CENTER;
        header.AddCell(cell);

        header.WriteSelectedRows(0, -1, document.LeftMargin, document.PageSize.Height - document.TopMargin + header.TotalHeight, writer.DirectContent);

        PdfPTable footer = new PdfPTable(1);
        footer.TotalWidth = document.PageSize.Width - document.LeftMargin - document.RightMargin;
        footer.DefaultCell.Border = Rectangle.NO_BORDER;

        cell = new PdfPCell(new Phrase("Footer"));
        cell.HorizontalAlignment = Element.ALIGN_CENTER;
        footer.AddCell(cell);

        footer.WriteSelectedRows(0, -1, document.LeftMargin, document.BottomMargin - footer.TotalHeight - 10, writer.DirectContent);
    }
}

然后，在創建PdfWriter對象時，將HeaderFooter實例傳遞給PdfWriter的setPageEvent方法：

PdfWriter writer = PdfWriter.GetInstance(document, new FileStream("output.pdf", FileMode.Create));
writer.PageEvent = new HeaderFooter();

通過這樣的方法，你可以在生成的PDF文檔中添加頁眉和頁腳。