Try adding font to Phrase constructors:
for (int j = 0; j < dataGridView1.Columns.Count; j++)
{
table.AddCell(new Phrase(dataGridView1.Columns[j].HeaderText,fontTable));
}
//..
for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
for (int k = 0; k < dataGridView1.Columns.Count; k++)
{
if (dataGridView1[k, i].Value != null)
{
table.AddCell(new Phrase(dataGridView1[k, i].Value.ToString(),fontTable));
}
}
}
Check this link for more info about Chunkc, Phrases etc. http://www.mikesdotnetting.com/Article/82/iTextSharp-Adding-Text-with-Chunks-Phrases-and-Paragraphs