Did you know that OpenType comes in two flavors? PostScript-flavored OpenType fonts have .otf endings and TrueType-flavored OpenType fonts have .ttf endings. Both flavors are cross-platform and can be installed on either a Mac or PC.
TrueType-flavored OpenType fonts will have an OT/TT badge and are optimal for programs— such as PowerPoint and Excel— that do not fully support all OpenType features.
While PostScript-flavored OpenType fonts will have an OT badge and works best in programs—like Adobe InDesign —that can support all OpenType features.
So if you are working with a client that uses MS Word and you recommend that they license an OpenType version of the font, please make sure that you let them know which flavor is best. We have a great post on FontFont’s OpenType formats you should read if you’re eager for an in-depth explanation that uses FF DIN as example.