> You need to tell Emacs to read the file with the correct decoding.  In
   > this case, I think this will do the trick:

   >   C-x RET c mac-roman RET C-x C-f FILE-NAME RET

That worked thank you!

    1. You did you guess mac-roman? How can I find out myself in the future?

    2. Is there any faster possibility? I tried out
       (set-buffer-file-coding-system 'mac nil) but this did not work,
       also there I did not find mac-roman as a coding system.

   > Maybe.  It depends on your locale defaults and on whether you
   > customized those defaults (with the likes of prefer-coding-system).
   > Not every encoding can be reliably decoded, if the defaults defeat
   > that.

   > One way of avoiding the manual specification of the encoding is to use
   > the coding: tag inside the file, either on the first line or in the
   > file-local variables.

That is what I usually do, but a tag in the first line but if I receive
a file whose coding I don't know and don't know how to find it out, I am
sort of stuck.