In Python 3, pass an appropriate errors= value (such as errors=ignore or errors=replace) on creating your file object (presuming it to be a subclass of io.TextIOWrapper — and if it isn’t, consider wrapping it in one!); also, consider passing a more likely encoding than charmap (when you aren’t sure, utf-8 is always a good place to start).
For instance:
f = open('misc-notes.txt', encoding='utf-8', errors="ignore")
In Python 2, the read() operation simply returns bytes; the trick, then, is decoding them to get them into a string (if you do, in fact, want characters as opposed to bytes). If you don’t have a better guess for their real encoding:
your_string.decode('utf-8', 'replace')
…to replace unhandled characters, or
your_string.decode('utf-8', 'ignore')
to simply ignore them.
That said, finding and using their real encoding (rather than guessing utf-8) would be preferred.