C# word或者excel儲存或匯出為PDF

需要實現一個功能，不利用第三方控制元件匯出PDF，後來發現excel或word自帶到處pdf

以下僅僅寫出word到處PDF，excel程式碼類似

                Word.Application app = new Word.Application();
                Word.Document doc = app.Documents.Add();

                Word.Range range = doc.Paragraphs[1].Range;

                range.Text = txtText.Text;
                doc.ExportAsFixedFormat(sfd.FileName, Microsoft.Office.Interop.Word.WdExportFormat.wdExportFormatPDF);
                MessageBox.Show("Save pdf file success,file disk:" + sfd.FileName);