用Aspose在MS-Powerpoint中查找给定单词

我试图检查MS Powerpoint是否包含给定单词,但它不起作用。

这是我的班级,负责检查ppt文件:

public class FindContentOfPpt
{
    private static bool IsParagraphContain(IParagraph paragraph, string content)
    {
        return paragraph.Portions.Any(port => port.Text.Contains(content));
    }

    private static bool IsTextBoxContain(ITextFrame textBox, string content)
    {
        return textBox.Paragraphs.Any(para => IsParagraphContain(para, content));
    }

    private static bool IsSlideContain(ISlide slide, string content)
    {
        var allTextBoxes = SlideUtil.GetAllTextBoxes(slide);
        return allTextBoxes.Any(textBox => IsTextBoxContain(textBox, content));
    }

    public bool IsContain(string filePath, string content)
    {
        var pres = new Presentation(filePath);

        return pres.Slides.Any(slide => IsSlideContain(slide, content));
    }
}

var isContain = new FindContentOfPpt().IsContain("Find and Replace.pptx", "Presentation");

尽管我的ppt文件包含一个文本框,其中包含内容:“This is Presentation”(这是演示文稿),但is contain始终为false。我已经调试过了,类可以打开ppt文件,但是textbox值不正确。