Something like this:
Public Class Form1
Dim countLines As Int32
Dim array(10) As String
Sub PrintLines()
countLines = 0
' Loop over lines in TextBox.
For Each line As String In TextBox1.Text.Split(vbCrLf)
array(countLines) = line.Replace(vbLf, "")
countLines = countLines + 1
If countLines = 10 Then
countLines = 0
' Your print page routine here
System.Array.Clear(array, 0, 10)
End If
Next
If countLines > 0 Then
Console.WriteLine("Printing the last page ...")
' Your print page routine here
End If
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
' Create some test lines
For index = 1 To 35
TextBox1.Text = TextBox1.Text + "test " + index.ToString + vbCrLf
Next
PrintLines()
End Sub
End Class