OTF or TTF?
Font File formats come in basically two flavors these days: OTF (Open Type) and TTF (True Type). The TrueType format was jointly developed by Apple and Microsoft in the late 80s. Some years later, the OpenType format was jointly developed by Adobe and Microsoft.
The OpenType format has several exclusive and advanced capabilities including support for multiple platforms and expanded character sets. OpenType fonts can be used on either Macintosh or Windows operating systems. Additionally, the OpenType format permits the storage of up to 65,000 characters. This additional space provides type designers with the freedom to include add-ons such as small caps, old style figures, alternate characters and other extras that previously needed to be distributed as separate fonts.
However, not all OpenType fonts contain additional characters. Many fonts have been converted from either old PostScript or TrueType formats without expanded character sets to take advantage of the cross-platform functionality benefits of OpenType. Unless clearly stated otherwise, assume that the OpenType font you are purchasing features the traditional character set found in PostScript fonts. OpenType fonts that do contain expanded character sets are referred to informally as “OpenType Pro” fonts. Support for OpenType Pro fonts is increasing, yet the format is yet to be fully supported by all applications. To be safe, check the documentation of your applications. OpenType fonts install in the same manner as TrueType fonts.