Add Header and Footer for PDF using iTextsharp

As already answered by @Bruno you need to use pageEvents.

Please check out the sample code below:

private void CreatePDF()
{
    string fileName = string.Empty;    
    DateTime fileCreationDatetime = DateTime.Now;    
    fileName = string.Format("{0}.pdf", fileCreationDatetime.ToString(@"yyyyMMdd") + "_" + fileCreationDatetime.ToString(@"HHmmss"));    
    string pdfPath = Server.MapPath(@"~\PDFs\") +   fileName;

    using (FileStream msReport = new FileStream(pdfPath, FileMode.Create))
    {
        //step 1
        using (Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 140f, 10f))
        {
            try
            {
                // step 2
                PdfWriter pdfWriter = PdfWriter.GetInstance(pdfDoc, msReport);
                pdfWriter.PageEvent = new Common.ITextEvents();

                //open the stream 
                pdfDoc.Open();

                for (int i = 0; i < 10; i++)
                {
                    Paragraph para = new Paragraph("Hello world. Checking Header Footer", new Font(Font.FontFamily.HELVETICA, 22));    
                    para.Alignment = Element.ALIGN_CENTER;    
                    pdfDoc.Add(para);    
                    pdfDoc.NewPage();
                }

                pdfDoc.Close();    
            }
            catch (Exception ex)
            {
                //handle exception
            }    
            finally
            { 
            }    
        }    
    }
}

And create one class file named ITextEvents.cs and add following code:

public class ITextEvents : PdfPageEventHelper
{    
    // This is the contentbyte object of the writer
    PdfContentByte cb;

    // we will put the final number of pages in a template
    PdfTemplate headerTemplate, footerTemplate;

    // this is the BaseFont we are going to use for the header / footer
    BaseFont bf = null;

    // This keeps track of the creation time
    DateTime PrintTime = DateTime.Now;    

    #region Fields
    private string _header;
    #endregion

    #region Properties
    public string Header
    {
        get { return _header; }
        set { _header = value; }
    }
    #endregion    

    public override void OnOpenDocument(PdfWriter writer, Document document)
    {
        try
        {
            PrintTime = DateTime.Now;
            bf = BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1252, BaseFont.NOT_EMBEDDED);
            cb = writer.DirectContent;
            headerTemplate = cb.CreateTemplate(100, 100);
            footerTemplate = cb.CreateTemplate(50, 50);
        }
        catch (DocumentException de)
        {    
        }
        catch (System.IO.IOException ioe)
        {    
        }
    }

    public override void OnEndPage(iTextSharp.text.pdf.PdfWriter writer, iTextSharp.text.Document document)
    {
        base.OnEndPage(writer, document);    
        iTextSharp.text.Font baseFontNormal = new iTextSharp.text.Font(iTextSharp.text.Font.FontFamily.HELVETICA, 12f, iTextSharp.text.Font.NORMAL, iTextSharp.text.BaseColor.BLACK);    
        iTextSharp.text.Font baseFontBig = new iTextSharp.text.Font(iTextSharp.text.Font.FontFamily.HELVETICA, 12f, iTextSharp.text.Font.BOLD, iTextSharp.text.BaseColor.BLACK);    
        Phrase p1Header = new Phrase("Sample Header Here", baseFontNormal);

        //Create PdfTable object
        PdfPTable pdfTab = new PdfPTable(3);

        //We will have to create separate cells to include image logo and 2 separate strings
        //Row 1
        PdfPCell pdfCell1 = new PdfPCell();
        PdfPCell pdfCell2 = new PdfPCell(p1Header);
        PdfPCell pdfCell3 = new PdfPCell();
        String text = "Page " + writer.PageNumber + " of ";    

        //Add paging to header
        {
            cb.BeginText();
            cb.SetFontAndSize(bf, 12);
            cb.SetTextMatrix(document.PageSize.GetRight(200), document.PageSize.GetTop(45));
            cb.ShowText(text);
            cb.EndText();
            float len = bf.GetWidthPoint(text, 12);
            //Adds "12" in Page 1 of 12
            cb.AddTemplate(headerTemplate, document.PageSize.GetRight(200) + len, document.PageSize.GetTop(45));
        }
        //Add paging to footer
        {
            cb.BeginText();
            cb.SetFontAndSize(bf, 12);
            cb.SetTextMatrix(document.PageSize.GetRight(180), document.PageSize.GetBottom(30));
            cb.ShowText(text);
            cb.EndText();
            float len = bf.GetWidthPoint(text, 12);
            cb.AddTemplate(footerTemplate, document.PageSize.GetRight(180) + len, document.PageSize.GetBottom(30));
        }

        //Row 2
        PdfPCell pdfCell4 = new PdfPCell(new Phrase("Sub Header Description", baseFontNormal));

        //Row 3 
        PdfPCell pdfCell5 = new PdfPCell(new Phrase("Date:" + PrintTime.ToShortDateString(), baseFontBig));
        PdfPCell pdfCell6 = new PdfPCell();
        PdfPCell pdfCell7 = new PdfPCell(new Phrase("TIME:" + string.Format("{0:t}", DateTime.Now), baseFontBig));    

        //set the alignment of all three cells and set border to 0
        pdfCell1.HorizontalAlignment = Element.ALIGN_CENTER;
        pdfCell2.HorizontalAlignment = Element.ALIGN_CENTER;
        pdfCell3.HorizontalAlignment = Element.ALIGN_CENTER;
        pdfCell4.HorizontalAlignment = Element.ALIGN_CENTER;
        pdfCell5.HorizontalAlignment = Element.ALIGN_CENTER;
        pdfCell6.HorizontalAlignment = Element.ALIGN_CENTER;
        pdfCell7.HorizontalAlignment = Element.ALIGN_CENTER;    

        pdfCell2.VerticalAlignment = Element.ALIGN_BOTTOM;
        pdfCell3.VerticalAlignment = Element.ALIGN_MIDDLE;
        pdfCell4.VerticalAlignment = Element.ALIGN_TOP;
        pdfCell5.VerticalAlignment = Element.ALIGN_MIDDLE;
        pdfCell6.VerticalAlignment = Element.ALIGN_MIDDLE;
        pdfCell7.VerticalAlignment = Element.ALIGN_MIDDLE;    

        pdfCell4.Colspan = 3;  

        pdfCell1.Border = 0;
        pdfCell2.Border = 0;
        pdfCell3.Border = 0;
        pdfCell4.Border = 0;
        pdfCell5.Border = 0;
        pdfCell6.Border = 0;
        pdfCell7.Border = 0;    

        //add all three cells into PdfTable
        pdfTab.AddCell(pdfCell1);
        pdfTab.AddCell(pdfCell2);
        pdfTab.AddCell(pdfCell3);
        pdfTab.AddCell(pdfCell4);
        pdfTab.AddCell(pdfCell5);
        pdfTab.AddCell(pdfCell6);
        pdfTab.AddCell(pdfCell7);

        pdfTab.TotalWidth = document.PageSize.Width - 80f;
        pdfTab.WidthPercentage = 70;
        //pdfTab.HorizontalAlignment = Element.ALIGN_CENTER;    

        //call WriteSelectedRows of PdfTable. This writes rows from PdfWriter in PdfTable
        //first param is start row. -1 indicates there is no end row and all the rows to be included to write
        //Third and fourth param is x and y position to start writing
        pdfTab.WriteSelectedRows(0, -1, 40, document.PageSize.Height - 30, writer.DirectContent);
        //set pdfContent value

        //Move the pointer and draw line to separate header section from rest of page
        cb.MoveTo(40, document.PageSize.Height - 100);
        cb.LineTo(document.PageSize.Width - 40, document.PageSize.Height - 100);
        cb.Stroke();

        //Move the pointer and draw line to separate footer section from rest of page
        cb.MoveTo(40, document.PageSize.GetBottom(50) );
        cb.LineTo(document.PageSize.Width - 40, document.PageSize.GetBottom(50));
        cb.Stroke();
    }

    public override void OnCloseDocument(PdfWriter writer, Document document)
    {
        base.OnCloseDocument(writer, document);

        headerTemplate.BeginText();
        headerTemplate.SetFontAndSize(bf, 12);
        headerTemplate.SetTextMatrix(0, 0);
        headerTemplate.ShowText((writer.PageNumber - 1).ToString());
        headerTemplate.EndText();

        footerTemplate.BeginText();
        footerTemplate.SetFontAndSize(bf, 12);
        footerTemplate.SetTextMatrix(0, 0);
        footerTemplate.ShowText((writer.PageNumber - 1).ToString());
        footerTemplate.EndText();  
    }
}

I hope it helps!