使用同步将.ppt文件转换为 PDF 时出错

下面的代码可以将pptx文件转换为pdf，没有任何问题。

try
{
    //Opens the specified presentation
    IPresentation presentation = Presentation.Open(@"D:'YUs'Test'pp2.pptx");
    presentation.ChartToImageConverter = new ChartToImageConverter();
    presentation.ChartToImageConverter.ScalingMode = Syncfusion.OfficeChart.ScalingMode.Best;
    PresentationToPdfConverterSettings settings = new PresentationToPdfConverterSettings();
    settings.ShowHiddenSlides = true;
    PdfDocument doc = PresentationToPdfConverter.Convert(presentation, settings);
    doc.Save(@"D:'YUs'Test'pp2.pdf");
    doc.Close();
}
catch (Exception err)
{
    Response.Write("error when saving presentation file: " + err.ToString() + "<br/><br/><br/>");
}

但是当我尝试使用代码转换.ppt文件时，它返回此错误：

Syncfusion.Compression.Zip.ZipException: Zip exception.Can't locate end of central directory record. Possible wrong file format or archive is corrupt. at Syncfusion.Compression.Zip.ZipArchive.Open(Stream stream, Boolean closeStream) at Syncfusion.Presentation.FileDataHolder.Open(Stream stream) at Syncfusion.Presentation.Presentation.SetArchieveItems(Stream stream) at Syncfusion.Presentation.Presentation.ParseDocument(Stream fileStream) at Syncfusion.Presentation.Presentation.OpenAsStream(Stream stream) at Syncfusion.Presentation.Presentation.Open(String fileName) at PUBLIC_ConvertOfficeToPdfNetOffice.Page_Load(Object sender, EventArgs e) in d:'ConvertOfficeToPdfNetOffice.aspx.cs:line 30

我已经尝试过许多不同的PPT文件，但它总是会返回相同的错误。