How to print multiple pages using checkbox?

protected void btnPrint_Click(object sender, EventArgs e)
{
    PrintDocument pdoc = new PrintDocument();
    foreach (GridViewRow row in GVCloneList.Rows)
    {
       if (row.RowType == DataControlRowType.DataRow)
       {
           CheckBox chkRow = (row.Cells[0].FindControl("ChkPrnt") as CheckBox);
           if (chkRow.Checked)
           {
              String Id = chkRow.ToolTip;
              DataTable Dtable = clDl.Select(Convert.ToInt32(Id)).Tables[0];
              StringBuilder sb = new StringBuilder();
              string qs = "";
              try
              {
                // start creating page with title and date/time
                sb.Append("ID : " + Dtable.Rows[0]["Clone_Id"].ToString() + "\n\n");
               // iterate submitted form fields, also gets field name
               sb.Append("Species " + ": " + Dtable.Rows[0]["Species"].ToString() + "\n\n");
              sb.Append("Strain : " + Dtable.Rows[0]["Strain"].ToString() + "\n\n");
              sb.Append("Plasmid1 : " + Dtable.Rows[0]["Plasmid1"].ToString() + "\n\n");
              sb.Append("Plasmid2 : " + Dtable.Rows[0]["Plasmid2"].ToString() + "\n\n");
              sb.Append("Insert1 : " + Dtable.Rows[0]["Insert1"].ToString() + "\n\n");
              sb.Append("Insert2 : " + Dtable.Rows[0]["Insert2"].ToString() + "\n\n");
              sb.Append("Modifications : " + Dtable.Rows[0]["Modifications"].ToString() + "\n\n");
              sb.Append("Restrictions : " + Dtable.Rows[0]["Restrictions"].ToString() + "\n\n");
              sb.Append("Mutation " + ": " + Dtable.Rows[0]["Mutation"].ToString() + "\n\n");
              sb.Append("Antibiotic Resistance " + ": " + Dtable.Rows[0]["Antibiotic_Resistance"].ToString() + "\n\n");
   
              //sb.Append("Growth Conditions " + ": " + Dtable.Rows[0]["Growth_Conditions"].ToString() + "\n\n");

              sb.Append("Growth_Conditions :\n");
              sb.Append(Dtable.Rows[0]["Growth_Conditions"].ToString() + "\n\n");
              sb.Append("Others " + ": " + Dtable.Rows[0]["Others"].ToString() + "\n\n");
              sb.Append("Genotype " + ": " + Dtable.Rows[0]["Genotype"].ToString() + "\n\n");
              sb.Append("Risk Group " + ": " + Dtable.Rows[0]["Risk_Group"].ToString() + "\n\n");

              sb.Append("Source generatedby" + ": " + Dtable.Rows[0]["Source_generatedby"].ToString() + "\n\n");
              
              sb.Append("Source deliveredby " + ": " + Dtable.Rows[0]["Source_deliveredby"].ToString() + "\n\n");

              sb.Append("Acheivedby " + ": " + Dtable.Rows[0]["Acheivedby"].ToString() + "\n\n");

              sb.Append("Date " + ": " + Dtable.Rows[0]["Clone_Date"].ToString() + "\n\n");
              sb.Append("Box " + ": " + Dtable.Rows[0]["Box"].ToString() + "\n\n");
   
              // place stringbuilder in string reader
              stringToPrint = new StringReader(sb.ToString());
   
              // set font and size here
              printFont = new Font("Arial", 12);
              PrintDocument doc = new PrintDocument();
  
              // set the printer name
             //PrinterSettings.StringCollection Sc = PrinterSettings.InstalledPrinters;
             doc.PrinterSettings.PrinterName = doc.PrinterSettings.PrinterName;

            // add print page event handler
            doc.PrintPage += new PrintPageEventHandler(doc_PrintPage);
            // print the page
            doc.Print();
            // adds status to querystring 
        }
        catch
        {
        }
        finally
        {
            stringToPrint.Close();
         }
         // redirects to result.aspx
         //RNDprintdetails.DataSource = Dtable;
         //RNDprintdetails.DataBind();
         //ScriptManager.RegisterClientScriptBlock(this.Page, this.GetType(), "MyFun1", "printDiv('rndListPrint');", true);
        }
      }
     }
   }