求c#中，PDF转换word的程序，最好有详细代码

 Word.Application newApp = new Word.Application();                    // 指定原文件路径
                    Source = this.txtFileName.Text;
                    //目标文件路径
                    Target = saveFileDialog1.FileName;
                    // 缺省参数   
                    object Unknown = Type.Missing;                    //为了保险,只读方式打开
                    object readOnly = true; AcroBrokerLib.BrokerClass bc = new AcroBrokerLib.BrokerClass(); bc.BrokerFS_open();                    // 打开doc文件
                    Word.Document doc = newApp.Documents.Open(ref Source, ref Unknown,
                    ref readOnly, ref Unknown, ref Unknown,
                    ref Unknown, ref Unknown, ref Unknown,
                    ref Unknown, ref Unknown, ref Unknown,
                    ref Unknown, ref Unknown, ref Unknown,
                    ref Unknown, ref Unknown);
                    // 指定另存为格式(rtf)
                    object format;
                    
                    if (cboType.Text == "Wrod转PDF")
                    {
                        format = Word.WdSaveFormat.wdFormatPDF;
                    }
                    //else
                    //{
                    //    format = Word.WdSaveFormat.wdFormatDocument;
                    //}
                    if (File.Exists(Target.ToString()))
                    {
                        File.Delete(Target.ToString());
                    }
                    // 转换格式(另存为)
                    doc.SaveAs(ref Target, ref format,
                    ref Unknown, ref Unknown, ref Unknown,
                    ref Unknown, ref Unknown, ref Unknown,
                    ref Unknown, ref Unknown, ref Unknown,
                    ref Unknown, ref Unknown, ref Unknown,
                    ref Unknown, ref Unknown);                    // 关闭文档和Word程序
                    doc.Close(ref Unknown, ref Unknown, ref Unknown);
                    newApp.Quit(ref Unknown, ref Unknown, ref Unknown);                    doc = null;                    MessageBox.Show("转化成功。", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    txtFileName.Text = "";
                }
                catch (Exception ex)
                { 
                    
                }