First you will need to have the fonts that were used in your received attachment. Write them down, it should tell you what they were. Either, have your sender email the fonts to you or find them on a font website. (
www.dafont.com )
Secondly, once you've downloaded them, simply go to your fontbook. Applications>Font Book.app and install them from the location they were saved on your HD.
(others will suggest to use something other than FontBook but i think if you are not managing thousands of fonts... FontBook will work just fine.)
Good luck.