Public Class Form1
    Dim xlslist, pdflist As New List(Of String)
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        Dim path As String = Textbox1.text
        GetFiles(path, ListBox1, xlslist, "*.xls")
        GetFiles(path, ListBox2, pdflist, "*.pdf")
    End Sub
    Private Sub GetFiles(ByVal path As String, ByVal lb As ListBox, ByVal fl As _
      List(Of String), ByVal ext As String)
        If IO.Directory.Exists(path) Then
            fl.Clear()
            lb.Items.Clear()
            fl.AddRange(IO.Directory.GetFiles(path, ext, _
              IO.SearchOption.AllDirectories))
            For Each s As String In fl
                lb.Items.Add(IO.Path.GetFileName(s))
            Next
        End If
    End Sub
 
    Private Sub ListBox_MouseDoubleClick(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.MouseEventArgs) Handles _
    ListBox1.MouseDoubleClick, ListBox2.MouseDoubleClick
        Dim lb As ListBox = CType(sender, ListBox)
        If lb.IndexFromPoint(e.X, e.Y) > -1 Then
            Select Case lb.Name
                Case "ListBox1" : Process.Start(xlslist(lb.IndexFromPoint(e.X, _
                  e.Y)))
                Case "ListBox2" : Process.Start(pdflist(lb.IndexFromPoint(e.X, _
                e.Y)))
            End Select
        End If
    End Sub
End Class