无法访问关闭的流Itext7

Question

我正在使用itext7进行PDF操作。我正在尝试通过field.setValue方法填充表单字段。我的_Reader对象在构造函数级别填充，并用于添加和获取表单字段。但是在保存表单字段值时，在关闭PdfDocument对象时会捕获以下异常：

at System.IO.__Error.StreamIsClosed()
at System.IO.MemoryStream.Write(Byte[] buffer, Int32 offset, Int32 count)
at iText.IO.Source.OutputStream`1.Write(Byte[] b, Int32 off, Int32 len)
at iText.IO.Source.OutputStream`1.WriteInteger(Int32 value)
at iText.Kernel.Pdf.PdfWriter.WriteToBody(PdfObject pdfObj)
at iText.Kernel.Pdf.PdfWriter.FlushObject(PdfObject pdfObject, Boolean 
canBeInObjStm)
at iText.Kernel.Pdf.PdfDocument.FlushObject(PdfObject pdfObject, Boolean 
canBeInObjStm)
at iText.Kernel.Pdf.PdfObject.Flush(Boolean canBeInObjStm)
at iText.Kernel.Pdf.PdfPage.Flush(Boolean flushResourcesContentStreams)
at iText.Kernel.Pdf.PdfPage.Flush()
at iText.Kernel.Pdf.PdfDocument.Close()

代码段如下：

using (var memoryStream = new MemoryStream())
        {
            PdfDocument document = new PdfDocument(_Reader, new PdfWriter(memoryStream));
            PdfAcroForm Form = PdfAcroForm.GetAcroForm(document, true);
            foreach (PDFField Field in PDFFields)
            {
                PdfFormField formField = Form.GetField(Field.Name);

                switch (Field.Type)
                {
                    case PDF_FIELD_TYPE.TEXTBOX:
                        if (!string.IsNullOrEmpty(Field.Value))
                            formField.SetValue(Field.Value);
                        else
                            formField.SetValue(string.Empty);
                        break;
                }
            }
            document.Close();
            byte[] PDFBytes = ((MemoryStream)memoryStream).ToArray();

预先感谢您的帮助。