if you want to add blank row as i understand please: Try this:
PdfPTable table = new PdfPTable(3);
PdfPCell cell = new PdfPCell(new Phrase("Header spanning 3 columns"));
cell.Colspan = 3;
cell.HorizontalAlignment = 1; //0=Left, 1=Centre, 2=Right
table.AddCell(cell);
table.AddCell("Col 1 Row 1");
table.AddCell("Col 2 Row 1");
table.AddCell("Col 3 Row 1");
PdfPCell cellBlankRow = new PdfPCell(new Phrase(" "));
cell.Colspan = 3;
cell.HorizontalAlignment = 1;
table.AddCell(cellBlankRow);
table.AddCell("");
table.AddCell("");
table.AddCell("Col 1 Row 2");
table.AddCell("Col 2 Row 2");
table.AddCell("Col 3 Row 2");
Just insert blank rows using Phrase
. I have tested and works fine..! If i am misunderstand please let me know..!