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 me resolve the error.

The following line causes the error (line 6 in Public Class Form1):

cmd.OpenFile()

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Full 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

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Public Class Form1
Private Sub btnOK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOK.Click
        If radPDF1.Checked = True Then
            Dim fileName As String
            Dim cmd As New Commands
            cmd.OpenFile()
            If radPDF1.Checked = True Then
                fileName = "c:\test_3\johnson.pdf"
            Else
                fileName = "c:\test_3\ross.pdf"
            End If
        End If
    End Sub
End Class

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The following code runs without any errors.

Public Class Form1
    Public Sub OpenFile(ByVal AFileName As String)
        Dim psi As New ProcessStartInfo()
        psi.UseShellExecute = True
        psi.FileName = AFileName
        Process.Start(psi)
    End Sub

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    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOK.Click

        Dim fileName As String
        If radPDF1.Checked = True Then
            fileName = "c:\test_3\johnson.pdf"
        Else
            fileName = "c:\test_3\ross.pdf"
        End If
        OpenFile(fileName)
    End Sub

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