如何在Word中插入页脚?

我用它打开Word中的RTF并将其保存为PDF:

                Object oMissing = System.Reflection.Missing.Value;    //null for VB
                Object oTrue = true;
                Object oFalse = false;

                Microsoft.Office.Interop.Word.Application oWord = new Microsoft.Office.Interop.Word.Application();
                Microsoft.Office.Interop.Word.Document oWordDoc = new Microsoft.Office.Interop.Word.Document();

                oWord.Visible = false;
                Object rtfFile = filename;
                Object saveLoc = sfd.FileName;
                Object wdFormatPDF = 17;    //WdSaveFormat Enumeration
                oWordDoc = oWord.Documents.Add(ref rtfFile, ref oMissing, ref oMissing, ref oMissing);
                oWordDoc.SaveAs(ref saveLoc, ref wdFormatPDF, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing,
                     ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing);

                oWordDoc.Close(ref oFalse, ref oMissing, ref oMissing);
                oWord.Quit(ref oFalse, ref oMissing, ref oMissing);

但我也需要在每一页上插入一个页脚。我该怎么做?