Private Sub loadButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles loadButton.Click

    ' Displays an OpenFileDialog so the user can select a Cursor.
    Dim openFileDialog1 As New OpenFileDialog()
    openFileDialog1.Filter = "Cursor Files|*.txt"
    openFileDialog1.Title = "Select a Cursor File"

    If openFileDialog1.ShowDialog() = System.Windows.Forms.DialogResult.OK Then
        ' Assign the cursor in the Stream to the Form's Cursor property.
        Me.mainRTBox = New Text(openFileDialog1.OpenFile())
    End If

End Sub

Public Class Form1

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        ' Displays an OpenFileDialog so the user can select a Cursor.
        Dim openFileDialog1 As New OpenFileDialog()
        openFileDialog1.Filter = "Cursor Files|*.cur"
        openFileDialog1.Title = "Select a Cursor File"

        If openFileDialog1.ShowDialog() = System.Windows.Forms.DialogResult.OK Then
            ' Assign the cursor in the Stream to the Form's Cursor property.

            Dim extension = openFileDialog1.FileName.Substring(openFileDialog1.FileName.LastIndexOf("."))

            If extension Is "cur" Then
                Me.mainRTBox.Text = FileIO.FileSystem.ReadAllText(openFileDialog1.FileName)
            End If

        End If
    End Sub
End Class

RichTextBox1.LoadFile("YOUR DIRECTORY", RichTextBoxStreamType.RichText)

RichTextBox1.LoadFile("YOUR DIRECTORY", RichTextBoxStreamType.PlainText)