The OTF files are a newer type of font file that contains both printer and screen font data in one single component.or, in layman's terms: they're a bit more user friendly.

When possible, look in the folder for the font file that ends with '.otf' (Open Type Fonts) over the ones that end with '.ttf' (True Type Fonts).Some fonts do not have a folder, but rather just their own file in either the OTF or TTF formats (which is explained in the next bullet point).