PPT转PDF成功，但是转换出的pdf文件为空

[hxzz0190315]

请问使用网上找到的C#的ppt转pdf的代码，如下所示，为什么转换成功了，但是转换出来的pdf的文件大小只有不到1k，然后里面是空的呢？

using System.Web.UI;
using System.Web.UI.WebControls;
using System.Diagnostics;
using Word = Microsoft.Office.Interop.Word;
using Excel = Microsoft.Office.Interop.Excel;
using PowerPoint = Microsoft.Office.Interop.PowerPoint;
using Microsoft.Office.Core;

PPTConvertToPDF("C:/test.pptx", "C:/test.pdf");

    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();
                GC.Collect();
                GC.WaitForPendingFinalizers();
            }
            return result;
        }