public class RichTextBoxPrintCtrl : RichTextBox

    {

        //private const double anInch = 14.4;

        private const double anInch1 = 150;

        private const double anInch2 = 200;

        [StructLayout(LayoutKind.Sequential)]

        private struct RECT

        {

            public int Left;

            public int Top;

            public int Right;

            public int Bottom;

        }

        [StructLayout(LayoutKind.Sequential)]

        private struct CHARRANGE

        {

            public int cpMin;         //First character of range (0 for start of doc)

            public int cpMax;         //Last character of range (-1 for end of doc)

        }

        [StructLayout(LayoutKind.Sequential)]

        private struct FORMATRANGE

        {

            public IntPtr hdc;             //Actual DC to draw on

            public IntPtr hdcTarget;       //Target DC for determining text formatting

            public RECT rc;                //Region of the DC to draw to (in twips)

            public RECT rcPage;            //Region of the whole DC (page size) (in twips)

            public CHARRANGE chrg;         //Range of text to draw (see earlier declaration)

        }

        private const int WM_USER = 0x0400;

        private const int EM_FORMATRANGE = WM_USER + 57;

        [DllImport("USER32.dll")]

        private static extern IntPtr SendMessage(IntPtr hWnd, Int32 msg, Int32 wParam, Int32 lParam);

        public int PrintImage(int nStartFrom, Graphics g)

        {

            RECT rcToPrint = default(RECT);

            FORMATRANGE fr = default(FORMATRANGE);

            IntPtr iptHdc = IntPtr.Zero;

            IntPtr iptRes = IntPtr.Zero;

            IntPtr iptParam = IntPtr.Zero;

            // Calculate the area to render and print

            rcToPrint.Top = 0;

            rcToPrint.Bottom = (int)Math.Ceiling((g.VisibleClipBounds.Height * anInch2));

            rcToPrint.Left = 0;

            rcToPrint.Right = (int)Math.Ceiling((g.VisibleClipBounds.Width * anInch1));

            iptHdc = g.GetHdc();

            //Indicate character from to character to

            fr.chrg.cpMin = nStartFrom;

            fr.chrg.cpMax = -1;

            //Use the same DC for measuring and rendering point at printer hDC

            fr.hdc = fr.hdcTarget = iptHdc;

            //Indicate the area on page to print

            fr.rc = rcToPrint;

            //Get the pointer to the FORMATRANGE structure in memory

            iptParam = Marshal.AllocCoTaskMem(Marshal.SizeOf(fr));

            Marshal.StructureToPtr(fr, iptParam, false);

            //Send the rendered data for printing

            iptRes = SendMessage(this.Handle, EM_FORMATRANGE, 1, iptParam.ToInt32());

            //Free the block of memory allocated

            Marshal.FreeCoTaskMem(iptParam);

            //Release the device context handle obtained by a previous call

            g.ReleaseHdc(iptHdc);

            //Return last + 1 character printer

            return iptRes.ToInt32();

        }

    }

Bitmap imageText = new Bitmap(richTextBoxPrintCtrl1.Width, richTextBoxPrintCtrl1.Height);

                Graphics g = Graphics.FromImage(imageText);

                richTextBoxPrintCtrl1.PrintImage(0, g);