VB.net program to grab lines from files that contain a certain text pattern

I have the following code that iterates thru files ending in .dat within a folder. Now what I want to do is go into each file and grab one line at a time, and if that line contains "PO-", then I want to put it into an array. I'm thinking I need another loop (maybe another Next loop?). Can someone help me to grab lines containing "PO-" within these files and put them into an array? Thanks!

    Private Sub btnSaveReport_Click(sender As Object, e As EventArgs) Handles btnSaveReport.Click
        Try
            Dim arrayPOentries() As String
            Dim strSourceFileLocation As String = AppDomain.CurrentDomain.BaseDirectory + "_data/"
            Dim strDetinationFileLocation As String = tbSaveFileLocation.Text
            Dim Paths() As String = IO.Directory.GetFiles(strSourceFileLocation, "*.dat")
            For Each Path As String In Paths
                'another loop here?
            Next
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
        Me.Close()
    End Sub