Dim oFileStream As System.IO.FileStream = System.IO.File.OpenRead(sFileName)
Dim oStreamReader As New System.IO.StreamReader(oFileStream)
Dim sOldText As String = oStreamReader.ReadToEnd
oStreamReader.Close()
oFileStream.Close()
Dim sNewText As String
sNewText = Replace(sOldText, "ä", "ä")
System.IO.File.WriteAllText("C:\...\NewText.txt", sNewText)