Option Explicit
 
Private Sub Command1_Click()
    Dim ff1 As Integer
    Dim ff2 As Integer
    Dim s As String
 
    ff1 = FreeFile
    Open App.Path + "\Test1.txt" For Input As #ff1
    ff2 = FreeFile
    Open App.Path + "\Test2.txt" For Append As #ff2
    Do While Not EOF(ff1)
        Input #ff1, s
        If Mid(s, 341, 1) = "A" Then Mid(s, 341, 1) = "1"
        If Mid(s, 341, 1) = "B" Then Mid(s, 341, 1) = "2"
        If Mid(s, 341, 1) = "C" Then Mid(s, 341, 1) = "3"
        'und so weiter
        Print #ff2, s
    Loop
    Close ff1
    Close ff2
    Kill App.Path + "\Test1.txt"
    Name App.Path + "\Test2.txt" As App.Path + "\Test1.txt"
End Sub

Gru? Michi aus Hannover

1 + 1 = 3 f?r hinreichend gro?e 1