PdfPCell yourCell = new PdfPCell();
Paragraph yourParagraph = new Paragraph("Some Text:", FontFactory.GetFont("Calibri", 11f, Font.BOLD, BaseColor.BLACK));
LineSeparator underline = new LineSeparator(1, 100, BaseColor.BLACK, Element.ALIGN_LEFT, -2);
yourParagraph.Add(underline );
yourCell.AddElement(yourParagraph);
yourCell.PaddingTop = 20f;
yourCell.Border = PdfPCell.NO_BORDER;
yourTable.AddCell(yourCell);