Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button1.Click
        If TextBox1_Eingabe.Visible = True Then
            TextBox1_Eingabe.AppendText("3")
        End If
        If RichTextBox1_Eingabeninfo.Visible = True Then
            RichTextBox1_Eingabeninfo.AppendText("3")
        End If
    End Sub