Private Sub Command1_Click()
On Error GoTo ErrorDeImpresion
Printer.Print ""
RichTextBox1.SelPrint Printer.hDC
Printer.EndDoc
Exit Sub
ErrorDeImpresion:
Exit Sub
End Sub

En el Formulario [Form1 por defecto] :
Private Sub Form_Load() 
     Dim LineWidth As Long
     Me.Caption = "Rich Text Box Ejemplo de Impresion"
     Command1.Move 10, 10, 600, 380
     Command1.Caption = "&Imprimir"
     RichTextBox1.SelFontName = "Verdana, Tahoma, Arial"
     RichTextBox1.SelFontSize = 10
     LineWidth = WYSIWYG_RTF(RichTextBox1, 1440, 1440)
     Me.Width = LineWidth + 200
End Sub 

Private Sub Form_Resize() 
     RichTextBox1.Move 100, 500, Me.ScaleWidth - 200, Me.ScaleHeight - 600
End Sub 

Private Sub Command1_Click() 
     PrintRTF RichTextBox1, 1440, 1440, 1440, 1440
End Sub 

Crear un módulo y escribir:

Private Type Rect
Left As Long
Top As Long
Right As Long
Bottom As Long
End Type

Private Type CharRange
cpMin As Long
cpMax As Long
End Type

Private Type FormatRange
hdc As Long
hdcTarget As Long
rc As Rect
rcPage As Rect
chrg As CharRange
End Type

Private Const WM_USER As Long = &H400
Private Const EM_FORMATRANGE As Long = WM_USER + 57
Private Const EM_SETTARGETDEVICE As Long = WM_USER + 72
Private Const PHYSICALOFFSETX As Long = 112
Private Const PHYSICALOFFSETY As Long = 113
Private Declare Function GetDeviceCaps Lib "gdi32" ( _
ByVal hdc As Long, ByVal nIndex As Long) As Long
Private Declare Function SendMessage Lib "USER32" Alias "SendMessageA" _
(ByVal hWnd As Long, ByVal msg As Long, ByVal wp As Long, lp As Any) As Long
Private Declare Function CreateDC Lib "gdi32" Alias "CreateDCA" _
(ByVal lpDriverName As String, ByVal lpDeviceName As String, _
ByVal lpOutput As Long, ByVal lpInitData As Long) As Long

Public Function WYSIWYG_RTF(RTF As RichTextBox, LeftMarginWidth As Long, _
RightMarginWidth As Long) As Long
Dim LeftOffset As Long, LeftMargin As Long, RightMargin As Long
Dim LineWidth As Long
Dim PrinterhDC As Long
Dim r As Long
Printer.Print Space(1)
Printer.ScaleMode = vbTwips
LeftOffset = Printer.ScaleX(GetDeviceCaps(Printer.hdc, _
PHYSICALOFFSETX), vbPixels, vbTwips)
LeftMargin = LeftMarginWidth - LeftOffset
RightMargin = (Printer.Width - RightMarginWidth) - LeftOffset
LineWidth = RightMargin - LeftMargin
PrinterhDC = CreateDC(Printer.DriverName, Printer.DeviceName, 0, 0)
r = SendMessage(RTF.hWnd, EM_SETTARGETDEVICE, PrinterhDC, _
ByVal LineWidth)
Printer.KillDoc
WYSIWYG_RTF = LineWidth
End Function

Public Sub PrintRTF(RTF As RichTextBox, LeftMarginWidth As Long, _
TopMarginHeight, RightMarginWidth, BottomMarginHeight)
Dim LeftOffset As Long, TopOffset As Long
Dim LeftMargin As Long, TopMargin As Long
Dim RightMargin As Long, BottomMargin As Long
Dim fr As FormatRange
Dim rcDrawTo As Rect
Dim rcPage As Rect
Dim TextLength As Long
Dim NextCharPosition As Long
Dim r As Long
Printer.Print Space(1)
Printer.ScaleMode = vbTwips
LeftOffset = Printer.ScaleX(GetDeviceCaps(Printer.hdc, _
PHYSICALOFFSETX), vbPixels, vbTwips)
TopOffset = Printer.ScaleY(GetDeviceCaps(Printer.hdc, _
PHYSICALOFFSETY), vbPixels, vbTwips)
LeftMargin = LeftMarginWidth - LeftOffset
TopMargin = TopMarginHeight - TopOffset
RightMargin = (Printer.Width - RightMarginWidth) - LeftOffset
BottomMargin = (Printer.Height - BottomMarginHeight) - TopOffset
rcPage.Left = 0
rcPage.Top = 0
rcPage.Right = Printer.ScaleWidth
rcPage.Bottom = Printer.ScaleHeight
rcDrawTo.Left = LeftMargin
rcDrawTo.Top = TopMargin
rcDrawTo.Right = RightMargin
rcDrawTo.Bottom = BottomMargin
fr.hdc = Printer.hdc
fr.hdcTarget = Printer.hdc
fr.rc = rcDrawTo
fr.rcPage = rcPage
fr.chrg.cpMin = 0
fr.chrg.cpMax = -1
TextLength = Len(RTF.Text)
Do
NextCharPosition = SendMessage(RTF.hWnd, EM_FORMATRANGE, True, fr)
If NextCharPosition >= TextLength Then Exit Do
fr.chrg.cpMin = NextCharPosition
Printer.NewPage
Printer.Print Space(1)
fr.hDC = Printer.hDC
fr.hDCTarget = Printer.hDC
Loop
Printer.EndDoc
r = SendMessage(RTF.hWnd, EM_FORMATRANGE, False, ByVal CLng(0))
End Sub