Check if Textfile.txt Contain Certain Strings

I am creating a system to validate if a text file contains this serial number, if it contains it opens to Form2.

I have already created a part of the code that validates if the file exists, if it does not exist it creates.

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        Dim filepath As String = "License.txt"

        If Not System.IO.File.Exists(filepath) Then
          System.IO.File.Create(filepath).Dispose()
        End If

End Sub