คือ เวลารันโค้ด มันช้ามาก อาจจะเป็นเพราะมันต้องมีการ Random ด้วยครับ
อยากจะนำ task มาใช้ เช่น รันข้อมูลแต่ละหน้าพร้อมกัน เมื่อครบทุกหน้าก็ค่อย ปริ้น แบบนี้ครับ

อาจจะไม่ต้องใช้ PrintDocument  ใช้ tool อื่นก็ได้ ครับ ขอแค่เร็วขึ้นก็พอ ครับ
// เนื้อาแต่ละหน้าประมาณนี้ครับ


โค้ดครับ
[Spoil] คลิกเพื่อดูข้อความที่ซ่อนไว้namespace TestMath_TOR.Classed
{

    public class PrintAddDif
    {
        #region Variables
        private PrintDocument _printDocument = new PrintDocument();
        private string _ReportHeader,_ReportFooter;
        bool _bLandscape;
        private Font fontHeader = new Font("cordia new", 28, FontStyle.Bold);
        private Font fontDetail = new Font("cordia new", 48);
      
        System.Drawing.StringFormat strFormat; //Used to format the grid rows.
        int CountPage = 1; int Max; int Min;
        #endregion
        public PrintAddDif(string ReportHeader,string ReportFooter, int _min = 1, int _max = 10, int pCount = 1)
        {
            Min = _min; Max = _max; CountPage = pCount;
            _printDocument.PrintPage += new PrintPageEventHandler(printDocument_PrintPage);
            _printDocument.BeginPrint += new PrintEventHandler(printDocument_BeginPrint);
            _ReportHeader = ReportHeader;
            _ReportFooter = ReportFooter;
            _bLandscape = false;
        }
        public void PrintForm()
        {
            System.Windows.Forms.PrintDialog printDialog = new System.Windows.Forms.PrintDialog();
            printDialog.Document = _printDocument;
            printDialog.UseEXDialog = true;
            //Get the document
            if (System.Windows.Forms.DialogResult.OK == printDialog.ShowDialog())
            {
                _printDocument.DefaultPageSettings.Landscape = _bLandscape;
                _printDocument.DocumentName = "แบบฝึกหัด" + string.Format("{0:yyyyMMdd hhmmss}", DateTime.Now);
                _printDocument.Print();
            }
        }
        #region Begin Print Event Handler

        private void printDocument_BeginPrint(object sender, PrintEventArgs e)
        {
            strFormat = new System.Drawing.StringFormat();
            strFormat.Alignment = System.Drawing.StringAlignment.Near;
            strFormat.LineAlignment = System.Drawing.StringAlignment.Center;
            strFormat.Trimming = System.Drawing.StringTrimming.EllipsisCharacter;

            bFirstPage = true;
            bNewPage = true;
        }
        #endregion
        int lnxFinal;
        int lnxStart_1 = 200;
        int IntYStart_1 = 200;
        bool bFirstPage = false, bNewPage = false;
       
        int iCount = 1;

        private void printDocumentNewPage(object sender, PrintPageEventArgs e)
        {
            lnxFinal = e.MarginBounds.Right + 60;
            string a, b;
            SizeF size;
            int lineH = 2;
            //Draw Table
          //  List<Task> tasks = new List<Task&gt);
            for (int i = 1; i < 5;i++)
            {
                /* tasks.Add(Task.Run(() => 
                 {*/
                     int  y = IntYStart_1 * i;
                     if (y < 1000)
                     { 
              //  int y = IntYStart_1 * i;
                IntNumber i_n = RandomNumber.NextIntNumber(Min, Max);
                a = string.Join(" ",i_n.Max.ToString().ToArray());
                System.Threading.Thread.Sleep(1000);
                b = string.Join(" ", i_n.Min.ToString().ToArray());
                size = e.Graphics.MeasureString(a.ToString(), fontDetail);
                e.Graphics.DrawString(a.ToString(), fontDetail, Brushes.Black, (lnxStart_1 + 150 - size.Width), y- (int)(size.Height/1.5));//size.Height
                e.Graphics.DrawLine(new Pen(Color.Black, lineH), new Point(lnxStart_1,y ), new Point(lnxStart_1 + 150, y));
                e.Graphics.DrawString((RandomNumber.NextNumber(1,1000)>500)?"+":"-", fontHeader, Brushes.Black, lnxStart_1 + 155, y-25);
                size = e.Graphics.MeasureString(b, fontDetail);
                e.Graphics.DrawString(b, fontDetail, Brushes.Black, (lnxStart_1 + 150 - size.Width), y-26 );

                i_n = RandomNumber.NextIntNumber(Min, Max);
                System.Threading.Thread.Sleep(1000);
                a = a = string.Join(" ", i_n.Max.ToString().ToArray());
                System.Threading.Thread.Sleep(1000);
                b = string.Join(" ", i_n.Min.ToString().ToArray());
                size = e.Graphics.MeasureString(a.ToString(), fontDetail);
                e.Graphics.DrawString(a.ToString(), fontDetail, Brushes.Black, (lnxStart_1 + 455 - size.Width) , y - (int)(size.Height/1.5));//size.Height
                e.Graphics.DrawLine(new Pen(Color.Black, lineH), new Point(lnxStart_1+300, y), new Point(lnxStart_1 + 450, y));
                        e.Graphics.DrawString((RandomNumber.NextNumber(1, 1000) > 500) ? "+" : "-", fontHeader, Brushes.Black, lnxStart_1 + 455, y - 25);
                size = e.Graphics.MeasureString(b, fontDetail);
                e.Graphics.DrawString(b, fontDetail, Brushes.Black, (lnxStart_1 + 455 - size.Width), y-26 );
                y = y+100;
                        e.Graphics.DrawLine(new Pen(Color.Black, lineH), new Point(lnxStart_1, y), new Point(lnxStart_1 + 150, y));
                        e.Graphics.DrawLine(new Pen(Color.Black, lineH), new Point(lnxStart_1 + 300, y), new Point(lnxStart_1 + 450, y));
                        y = y+10;
                        e.Graphics.DrawLine(new Pen(Color.Black, lineH), new Point(lnxStart_1, y), new Point(lnxStart_1 + 150, y));
                        e.Graphics.DrawLine(new Pen(Color.Black, lineH), new Point(lnxStart_1 + 300, y), new Point(lnxStart_1 + 450, y));               
                   }

              //  }));
            }
          // Task.WaitAll(tasks.ToArray());
           

            StringFormat sf = new StringFormat();
            sf.LineAlignment = StringAlignment.Center;
            sf.Alignment = StringAlignment.Center;

            //Draw Header
             size = e.Graphics.MeasureString(_ReportHeader, fontHeader);
            e.Graphics.DrawString(_ReportHeader, fontHeader, Brushes.Black, (_printDocument.DefaultPageSettings.PaperSize.Width - size.Width) / 2, 10);
            // e.Graphics.DrawString( _ReportHeader, fontHeader, Brushes.Black, 100, e.MarginBounds.Top - e.Graphics.MeasureString(_ReportHeader, fontHeader, e.MarginBounds.Width).Height - 13);
            // String strDate = DateTime.Now.ToLongDateString() + " " + DateTime.Now.ToShortTimeString();
            //Draw Footer
            // e.Graphics.DrawString(_ReportFooter, fontHeader, Brushes.Black, e.MarginBounds.Left + 100, e.MarginBounds.Bottom + 40);
             size = e.Graphics.MeasureString(_ReportFooter, fontHeader);
            e.Graphics.DrawString(_ReportFooter, fontHeader, Brushes.Black, (_printDocument.DefaultPageSettings.PaperSize.Width - size.Width) / 2, _printDocument.DefaultPageSettings.PaperSize.Height - 20);
            bNewPage = false;
       

        }
        #region Print Page Event
        private void printDocument_PrintPage(object sender, PrintPageEventArgs e)
        {
            //Loop till all the grid rows not get printed
            if (bFirstPage) printDocumentNewPage(sender, e);

            iCount++;
            //If more lines exist, print another page.
            e.HasMorePages = (iCount <=CountPage) ? true : false;
        }
        #endregion

    }

}