Creating a document with header using OpenXML SDK 2.5

I want to create a new document with headers and footers. This is the code I am trying but it is not showing any header in the document, whereas the body content is available.

using (WordprocessingDocument doc = WordprocessingDocument.Create(HttpContext.Current.Server.MapPath("~/QEC/Reports/reportXML.docx"), DocumentFormat.OpenXml.WordprocessingDocumentType.Document))
        {
            MainDocumentPart mainPart = doc.AddMainDocumentPart();

            HeaderPart hdrPart = mainPart.AddNewPart<HeaderPart>();
            hdrPart.Header = new Header();
            Paragraph hdrPara = hdrPart.Header.AppendChild(new Paragraph());
            Run paraRun = hdrPara.AppendChild(new Run());
            paraRun.AppendChild(new Text("Hello"));

            mainPart.Document = new DocumentFormat.OpenXml.Wordprocessing.Document();
            Body body = mainPart.Document.AppendChild(new Body());
            Paragraph para = body.AppendChild(new Paragraph());
            Run run = para.AppendChild(new Run());
            run.AppendChild(new Text("Done"));

        }