PSowmiya says:
Dim bf As itextsharp.text.pdf.BaseFont = itextsharp.text.pdf.BaseFont.CreateFont("", itextsharp.text.pdf.BaseFont.CP1252, itextsharp.text.pdf.BaseFont.EMBEDDED)
Dim Font As itextsharp.text.Font = New itextsharp.text.Font(bf, 10)
Dim cell As New PdfPCell(New Phrase(column.HeaderText, Font))
Change above code with below.
Dim bf As BaseFont = BaseFont.CreateFont("c:/windows/fonts/HARLOWSI.ttf", BaseFont.CP1252, BaseFont.EMBEDDED)
Dim Font As Font = New Font(bf, 10, Font.BOLD)
Dim cell As New PdfPCell(New Phrase(column.HeaderText, Font))