You can install a font with your word processing application on, but the font will not be available until the next time you launch the word processing program. Double click on the suitcase and open it. You see a font display like this. You may have one of these and be confused when you use it. The boxes tell you that this font does not offer that character.
Some fonts have no numbers or lack punctuation symbols.
The freeware PopChar can be really handy at this point. It shows you all the characters available in the selected font. If you add only one freeware product to your Mac, make it this one. I have had quite a few inquiries about how to get this font and other custom fonts. Install it from them as available.