How to create a nested column?

var subTable2 = new PdfPTable(new float[] { 100, 100, 100, 100, 100, 100,100,100 });
subTable2.TotalWidth = 510f;
subTable2.LockedWidth = true;
subTable2.DefaultCell.HorizontalAlignment = Element.ALIGN_CENTER;
subTable2.AddCell(new Phrase("Examination", time51));
subTable2.DefaultCell.HorizontalAlignment = Element.ALIGN_CENTER;
subTable2.AddCell(new Phrase("Board", time51));
subTable2.DefaultCell.HorizontalAlignment = Element.ALIGN_CENTER;
subTable2.AddCell(new Phrase("Month and Year of Passing", time51));
subTable2.DefaultCell.HorizontalAlignment = Element.ALIGN_CENTER;
subTable2.AddCell(new PdfPCell(new Phrase("Mark", time51)));
PdfPTable nested = new PdfPTable(1);
nested.AddCell("");
nested.AddCell("Obtained");
nested.AddCell("Out of");
PdfPCell nesthousing = new PdfPCell(nested);
nesthousing.Padding = 0f;
subTable2.AddCell(nesthousing);
subTable2.DefaultCell.HorizontalAlignment = Element.ALIGN_CENTER;
subTable2.AddCell(new Phrase("Percentage", time51));
subTable2.DefaultCell.HorizontalAlignment = Element.ALIGN_CENTER;
subTable2.AddCell(new Phrase("Calss/Grade", time51));
doc.Add(subTable2);

Please take a look at SimpleTable12. It creates a table that looks like this: simple_table12.pdf

Table example

You could still fine-tune the height of the cells by using a padding or by introducing descender/ascender info, but those are details. What matters is: how to organize the cells?

I've written this small convenience method:

public PdfPCell createCell(String content, int colspan, int rowspan, int border) {
    PdfPCell cell = new PdfPCell(new Phrase(content, font));
    cell.setColspan(colspan);
    cell.setRowspan(rowspan);
    cell.setBorder(border);
    cell.setHorizontalAlignment(Element.ALIGN_CENTER);
    return cell;
}

You pass some content, a colspan, a rowspan and border info and it creates you the PdfPCell you need. This allows us to create code that is easier to read:

public void createPdf(String dest) throws IOException, DocumentException {
    font = new Font(FontFamily.HELVETICA, 10);
    Document document = new Document();
    PdfWriter.getInstance(document, new FileOutputStream(dest));
    document.open();
    PdfPTable table = new PdfPTable(8);
    table.setWidthPercentage(100);
    table.addCell(createCell("Examination", 1, 2, PdfPCell.BOX));
    table.addCell(createCell("Board", 1, 2, PdfPCell.BOX));
    table.addCell(createCell("Month and Year of Passing", 1, 2, PdfPCell.BOX));
    table.addCell(createCell("", 1, 1, PdfPCell.TOP));
    table.addCell(createCell("Marks", 2, 1, PdfPCell.TOP));
    table.addCell(createCell("Percentage", 1, 2, PdfPCell.BOX));
    table.addCell(createCell("Class / Grade", 1, 2, PdfPCell.BOX));
    table.addCell(createCell("", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("Obtained", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("Out of", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("12th / I.B. Diploma", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("Aggregate (all subjects)", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("", 1, 1, PdfPCell.BOX));
    table.addCell(createCell("", 1, 1, PdfPCell.BOX));
    document.add(table);
    document.close();
}

As you can see, it's a matter of calculating the correct colspan and rowspan values, and applying the correct borders.