如何使用iTextSharp保存PDF的.MoreInfo属性？

    public class PdfEnricher
{
    readonly IFileSystem fileSystem;

    public PdfEnricher(IFileSystem fileSystem)
    {
        this.fileSystem = fileSystem;
    }

    public void Enrich(string pdfFile, Hashtable fields)
    {
        if (!fileSystem.FileExists(pdfFile)) return;

        var newFile = GetNewFileName(pdfFile);
        var stamper = GetStamper(pdfFile, newFile);

        SetFieldsAndClose(stamper, fields);
    }

    string GetNewFileName(string pdfFile)
    {
        return fileSystem.GetDirectoryName(pdfFile) + @\"\\NewFileName.pdf\";
    }

    static void SetFieldsAndClose(PdfStamper stamper, Hashtable fields)
    {
        stamper.MoreInfo = fields;
        stamper.FormFlattening = true;
        stamper.Close();
    }

    static PdfStamper GetStamper(string pdfFile, string newFile)
    {
        var reader = new PdfReader(pdfFile);
        return new PdfStamper(reader, new FileStream(newFile, FileMode.Create));
    }
}