office转pdf,该如何处理

office转pdf
代码如下，用同样的方式word和Excel都能转成功，就是这个ppt不行  
 protected void Button1_Click(object sender, EventArgs e)
        {
            if (PPTConvertToPDF("C:/1.pptx", "C:/1.pdf"))
            {
                this.Response.Write("<script language=javascript>alert('转换成功！');</script>");
            }
            else
            {
                this.Response.Write("<script language=javascript>alert('对不起，转换失败！');</script>");
            }

        }
        /// <summary>          
        /// 把PowerPoing文件转换成PDF格式文件          
        /// </summary>          
        /// <param name="sourcePath">源文件路径</param>          
        /// <param name="targetPath">目标文件路径</param>           
        /// <returns>true=转换成功</returns>          
        private bool PPTConvertToPDF(string sourcePath, string targetPath)
        {
            bool result;
            PowerPoint.PpSaveAsFileType targetFileType = PowerPoint.PpSaveAsFileType.ppSaveAsPDF;
            object missing = Type.Missing;
            PowerPoint.ApplicationClass application = null;
            PowerPoint.Presentation persentation = null;

            try
            {
                application = new PowerPoint.ApplicationClass();
                persentation = application.Presentations.Open(sourcePath, MsoTriState.msoTrue, MsoTriState.msoFalse, MsoTriState.msoFalse);
                persentation.SaveAs(targetPath, targetFileType, Microsoft.Office.Core.MsoTriState.msoTrue);

                result = true;
            }
            catch
            {
                result = false;
            }
            finally
            {
                if (persentation != null)
                {
                    persentation.Close();
                    persentation = null;
                }

                if (application != null)
                {
                    application.Quit();
                    application = null;
                }

                GC.Collect();
                GC.WaitForPendingFinalizers();