Why are no lyrics displayed for a MIDI file?
Many MIDI files (with a .mid file name extension) do not have lyrics. If there are not lyrics in the MIDI file, then there are no lyrics for Notation to display. All Karaoke files (with a .kar file name extension) do have lyrics. Notation will always display lyrics for Karaoke files, unless you have the "view lyrics" button (in the Text tab) toggled "off".
If you open a MIDI file that does not have lyrics, you can add lyrics yourself to that song using the Text -> Lyric tools in Musician or Composer.
If you open a MIDI file that you are certain has lyrics, but Notation does not display the lyrics, then use the Show/Hide Types of Objects command in the Format menu, and make sure that Show Lyrics has a check mark by it, because in some MIDI files the lyrics is in a separate track which is hidden.