font size is to big on itextsharp and side margin wont change

PdfPTable pdftable = new PdfPTable(GridView1.HeaderRow.Cells.Count);
foreach (TableCell headerCell in GridView1.HeaderRow.Cells)
{
    Font font = new Font();
    font.Color = new BaseColor(GridView1.HeaderStyle.ForeColor);

    PdfPCell pdfcell = new PdfPCell(new Phrase(headerCell.Text, font));
    pdfcell.BackgroundColor = new BaseColor(GridView1.HeaderStyle.BackColor);
    pdftable.AddCell(pdfcell); 
}       

foreach (GridViewRow gridViewRow in GridView1.Rows)
{
    foreach (TableCell tableCell in gridViewRow.Cells)
    {
        Font font = new Font();
        font.Color = new BaseColor(GridView1.RowStyle.ForeColor);

        PdfPCell pdfcell = new PdfPCell(new Phrase(tableCell.Text));
        pdfcell.BackgroundColor = new BaseColor(GridView1.RowStyle.BackColor);
        pdftable.AddCell(pdfcell);
    }
}

Document pdfDocument = new Document(PageSize.LETTER, 10f, 10f, 10f, 10f);
pdfDocument.SetPageSize(PageSize.LETTER.Rotate());
PdfWriter.GetInstance(pdfDocument, Response.OutputStream);
pdfDocument.Open();
float[] widths = new float[] { 1f, 2f,3f,10f,6f,4f}; // size per column
pdftable.SetWidths(widths);
pdfDocument.Add(pdftable);
pdfDocument.Close();
Response.ContentType = "application/pdf";
Response.AppendHeader("Content-disposition", "attachment;filename=jalisto.pdf");
Response.Write(pdfDocument);
Response.Flush();
Response.End();