VB.Net Argument not Specified for Parameter Error

I am trying to work with two radio buttons in a simple VB.net app that allows a user to select and open a PDF using the Process object. One PDF will be assigned to each radio button. The code is shown below. I get the following error: "Argument not specified for parameter ‘AFileName’ of ‘Public Sub OpenFile(AFileName As String)."

Please help resolve the error.

This is not homework for a class. It is self-study using books.

Code:

Public Class Commands
    Public Sub OpenFile(ByVal AFileName As String)
        Dim psi As New ProcessStartInfo()
        psi.UseShellExecute = True
        psi.FileName = AFileName
        Process.Start(psi)
    End Sub
End Class

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim fileName As String
        Dim Commands As New Commands
        If RadioButton1.Checked = True Then
            fileName = "c:\test_3\johnson.pdf"
        End If
        If RadioButton2.Checked = True Then
            '        Else
            fileName = "c:\test_3\ross.pdf"
        End If
        MessageBox.Show("File name is: " + fileName)
        Commands.OpenFile()
    End Sub
End Class

The following code causes the error:

Commands.OpenFile()