Illegal characters in path while converting HTML and chat into pdf file

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C#

ASP.NET

i made multiple pie chart dynamically and add them into a placeholder in C# .net, and now i m facing problem when i convert that page html into pdf file.

It show "Error!Illegal characters in path".

I searches any solution from few days.
Any one please suggest me any solution ASAP.

What I have tried:

Chart txtChart = new Chart();
txtChart.ID = "txtChart" + rowIndex;
txtChart.Titles.Add("Q.No." + formFieldData.Survey_FormFields_Order + ". " + formFieldData.Survey_FormFields_Text);
txtChart.Font.Bold = true;
txtChart.RenderType = RenderType.ImageTag;


DataTable dt = dtChart;
string[] x = new string[dt.Rows.Count];
int[] y = new int[dt.Rows.Count];
for (int i = 0; i < dt.Rows.Count; i++)
{
x[i] = dt.Rows[i][2].ToString();
y[i] = Convert.ToInt32(dt.Rows[i][3]);
}

Series txtSeries = new Series();
txtSeries.Name = "txtSeries" + rowIndex;
txtSeries.Points.DataBindXY(x, y);
txtSeries.ChartType = SeriesChartType.Pie;
txtSeries.LegendText = "#VALX";

foreach (DataPoint point in txtSeries.Points)
{
point.Label = "#PERCENT";
point.ToolTip = "#VALX\n#PERCENT";
}

Legend txtLegend = new Legend();
txtLegend.Name = "txtSeries" + rowIndex;
txtLegend.Alignment = System.Drawing.StringAlignment.Center;
txtLegend.Docking = Docking.Right;
txtLegend.IsTextAutoFit = false;
txtLegend.LegendStyle = LegendStyle.Column;
txtLegend.Enabled = true;
txtLegend.Title = _strResultOptions;// "overall results";
txtLegend.IsDockedInsideChartArea = false;

txtSeries.EmptyPointStyle.IsVisibleInLegend = false;
txtSeries.EmptyPointStyle.IsValueShownAsLabel = false;

ChartArea txtChartArea = new ChartArea();
txtChartArea.Name = "txtChartArea" + rowIndex;
txtChartArea.BorderWidth = 0;
txtChartArea.Area3DStyle.Enable3D = true;

txtChart.Series.Add(txtSeries);
txtChart.ChartAreas.Add(txtChartArea);
txtChart.Legends.Add(txtLegend);

txtChart.ImageType = System.Web.UI.DataVisualization.Charting.ChartImageType.Bmp;
txtChart.ImageStorageMode = ImageStorageMode.UseHttpHandler;

txtChart.Width = new System.Web.UI.WebControls.Unit(500, System.Web.UI.WebControls.UnitType.Pixel);
txtChart.Height = new System.Web.UI.WebControls.Unit(250, System.Web.UI.WebControls.UnitType.Pixel);

phChartArea.Controls.Add(txtChart);
phChartArea.Controls.Add(new LiteralControl(""));

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html into pdf file code
------------------------

System.IO.StringWriter stringWrite = new StringWriter();
System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);

phChartArea.RenderControl(htmlWrite);

StringReader reader = new StringReader(stringWrite.ToString());

Document doc = new Document(PageSize.A4);
HTMLWorker parser = new HTMLWorker(doc);
PdfWriter.GetInstance(doc, Response.OutputStream);
doc.Open();
parser.Parse(reader);
doc.Close();

Response.ContentType = "application/pdf";
Response.AddHeader("content-disposition", "attachment;filename=Chart.pdf");
Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.Write(doc);
Response.End();

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