Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button1.Click
        BackgroundWorker1.RunWorkerAsync()
End Sub

dim result as boolean = false
Dim sr As StreamReader = New StreamReader("C:\text.txt")
            filecontent = sr.ReadToEnd()
            sr.Close()
 
Select Case filecontent
Case "rot"
result = true
Case "gruen"
result = true
End Select

 Private Sub BackgroundWorker1_RunWorkerCompleted(ByVal sender As Object, ByVal _
   e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles _
   BackgroundWorker1.RunWorkerCompleted
 
if result = true then
label1.text = "Wort wurde gefunden!"
else
label1.text = "Nix gefunden!"
end if
 
    End Sub