using MSExcel = Microsoft.Office.Interop.Excel;

private bool exceltoPDF(string sourcePath, string targetPath)
        {
            bool result;
            object missing = Type.Missing;
            MSExcel.ApplicationClass application = null;
            MSExcel.Workbook workBook = null;
            try
            {
                application = new MSExcel.ApplicationClass();
                object target = targetPath;
                workBook = application.Workbooks.Open(sourcePath, missing, missing, missing, missing, missing,
                        missing, missing, missing, missing, missing, missing, missing, missing, missing);

                workBook.ExportAsFixedFormat(MSExcel.XlFixedFormatType.xlTypePDF, target, MSExcel.XlFixedFormatQuality.xlQualityStandard
                    , true, false, missing, missing, missing, missing);
                result = true;
            }
            catch
            {
                result = false;
            }
            finally
            {
                if (workBook != null)
                {
                    workBook.Close(true, missing, missing);
                    workBook = null;
                }
                if (application != null)
                {
                    application.Quit();
                    application = null;
                }
                GC.Collect();
                GC.WaitForPendingFinalizers();
            }
            return result;
        }