Using fonts background
From TeX on Mac OS X wiki
By default, most typesetting will use the Computer Modern fonts. The bitmap version of these fonts was specifically designed for use with TeX and typesetting originally required fonts to be in this format. Unfortunately, such fonts can look ugly on-screen if the viewer does not support them properly (although they will still look fine printed), so another font format is often a better choice. Today it is possible to use several other font formats with TeX and most current installations will therefore use one of the available postscript versions of Computer Modern by default.