并行循环抛出异常

Question

目前我正在开发一个Windows窗体应用程序。首先，我使用for循环，它工作得很好，但数据变得更大，并开始生成文件非常慢。我切换到并行循环，它在“document.Save（fileName +”。pdf“）上抛出并且异常”参数无效“;”

以下是我的代码片段

    private void btnGenerateFiles_Click(object sender, EventArgs e)
    {
        if (labelDataSrc.Text == string.Empty || labelTemplateSrcBG.Text == string.Empty)
        {
            MessageBox.Show("Template or Data files are not set");
            return;
        }

        ComponentInfo.SetLicense("FREE-LIMITED-KEY");

        DocumentModel document =  DocumentModel.Load(Globals.pathTemplateSrcBG); ;

        Excel.Application objExcel = new Excel.Application();
        objExcel.Visible = true;
        Excel.Workbook objBook = objExcel.Workbooks.Open(Globals.pathDataSrc);
        Excel.Worksheet objsheet = objBook.Worksheets["Sheet2"];

        var range = objsheet.UsedRange;
        var rCnt = range.Rows.Count;

        Parallel.For(2, rCnt, i =>
        {
            if (objsheet.Cells.get_Item(i, "D").Value == "BG")
            {
                document = DocumentModel.Load(Globals.pathTemplateSrcBG);
            }
            else if (objsheet.Cells.get_Item(i, "D").Value == "ENG")
            {
                document = DocumentModel.Load(Globals.pathTemplateSrcENG);
            }
            else if (objsheet.Cells.get_Item(i, "D").Value == "RO")
            {
                document = DocumentModel.Load(Globals.pathTemplateSrcRO);
            }
            else
            {
                MessageBox.Show("No language of communication on line " + i);
            }

            // Find and replace text.
            document.Content.Replace("*ClnName*", Convert.ToString(objsheet.Cells.get_Item(i, "A").Value) + " " + Convert.ToString(objsheet.Cells.get_Item(i, "B").Value));
            document.Content.Replace("*clnContractNum*", Convert.ToString(objsheet.Cells.get_Item(i, "F").Value));
            document.Content.Replace("*DateSigned*", DateTime.Now.ToString("dd.MM.yyyy"));

            string fileName = Convert.ToString(objsheet.Cells.get_Item(i, "F").Value).Replace(@"/", @"-");
            document.Save(fileName + ".pdf");

            labelProgress.Text = i + "/" + rCnt;
            Application.DoEvents();
        });
    }

很抱歉，如果我的问题很愚蠢，但是我正在敲打那个问题并在几小时内寻找解决方案。

提前致谢！