Code isn't drawing a horizontal line in my PDF

I'm trying to add a horizontal line on top to divide the header text from the actual values in my pdf file:

Here's my code:

public class StudentList
{
    public void PrintStudentList(int gradeParaleloID)
    {
        StudentRepository repo = new StudentRepository();
        var students = repo.FindAllStudents()
                            .Where(s => s.IDGradeParalelo == gradeParaleloID);

        try
        {
            Document document = new Document(PageSize.LETTER);

            PdfWriter writer = PdfWriter.GetInstance(document, new FileStream(Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory) + "\\Alumnos.pdf", FileMode.Create));
            document.Open();

            PdfContentByte cb = writer.DirectContent;
            cb.SetLineWidth(2.0f);   // Make a bit thicker than 1.0 default
            cb.SetGrayStroke(0.95f); // 1 = black, 0 = white
            cb.MoveTo(20, 30);
            cb.LineTo(400, 30);
            cb.Stroke();

            PdfPTable table = new PdfPTable(3);                
            float[] widths = new float[开发者_运维问答] { 0.6f, 0.75f, 2f };
            table.SetWidths(widths);
            PdfPCell numeroCell = new PdfPCell(new Phrase("Nro."));
            numeroCell.Border = 0;
            numeroCell.HorizontalAlignment = 0;
            table.AddCell(numeroCell);

            PdfPCell codigoCell = new PdfPCell(new Phrase("RUDE"));
            codigoCell.Border = 0;
            codigoCell.HorizontalAlignment = 0;
            table.AddCell(codigoCell);

            PdfPCell nombreCell = new PdfPCell(new Phrase("Apellidos y Nombres"));
            nombreCell.Border = 0;
            nombreCell.HorizontalAlignment = 0;
            table.AddCell(nombreCell);

            int c = 1;
            foreach (var student in students)
            {
                PdfPCell cell = new PdfPCell(new Phrase(c.ToString()));
                cell.Border = 0;
                cell.HorizontalAlignment = 0;
                table.AddCell(cell);

                cell = new PdfPCell(new Phrase(student.Rude.ToString()));
                cell.Border = 0;
                cell.HorizontalAlignment = 0;
                table.AddCell(cell);

                cell = new PdfPCell(new Phrase(student.LastNameFather + " " + student.LastNameMother + " " + student.Name));
                cell.Border = 0;
                cell.HorizontalAlignment = 0;
                table.AddCell(cell);
                c++;
            }
            table.SpacingBefore = 20f;
            table.SpacingAfter = 30f;

            document.Add(table);
            document.Close();
        }
        catch (DocumentException de)
        {
            Debug.WriteLine(de.Message);
        }
        catch (IOException ioe)
        {
            Debug.WriteLine(ioe.Message);
        }

    }
}

I don't understand why the cb.Stroke() isn't working. Any suggestions?

Drawing with iTextSharp's PdfContentByte class can be a little confusing. The height is actually relative to the bottom, not the top. So the top of the page is not 0f, but instead is actually document.Top, which on your page size of PageSize.LETTER is 726f. So if you want to draw your line 30 units from the top, try:

cb.MoveTo(20, document.Top - 30f);
cb.LineTo(400, document.Top - 30f);

Just curious -- why do it the hard way instead of using table borders? (I noticed you set your borders to 0) Trying to space out lines by hand is the biggest pain. If you ever move content in your PDF around, you'll have to make sure your measurements still work.

Try this:

numeroCell.Border = 0;
numeroCell.BorderColorBottom = new BaseColor(System.Drawing.Color.Black);
numeroCell.BorderWidthBottom = 1f;

codigoCell.Border = 0;
codigoCell.BorderColorBottom = new BaseColor(System.Drawing.Color.Black);
codigoCell.BorderWidthBottom = 1f;

nombreCell.Border = 0;
nombreCell.BorderColorBottom = new BaseColor(System.Drawing.Color.Black);
nombreCell.BorderWidthBottom = 1f;

That should give you a nice solid black line under your header row, no measurements needed: