Normally, Emacs knows when you are editing formatted text because it recognizes the special annotations used in the file that you visited. However, there are situations in which you must take special actions to convert file contents or turn on Enriched mode:
format-decode-buffer translates text in various
formats into Emacs's internal format. It asks you to specify the format
to translate from; however, normally you can type just RET, which
tells Emacs to guess the format.
If you wish to look at a file in text/enriched format in its raw form, as a sequence of characters with no formatting, use M-x format-find-file RET filename RET RET. The empty second argument means, "read without format conversion."