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There are two types, or flavors, of OpenType fonts (OTFs): PostScript flavored OTFs and TrueType flavored OTFs. Those with PostScript outlines are of the Compact Font Format (CFF) variety and are designated by the ".otf" suffix. Technically, all Windows TrueType fonts can be considered OpenType fonts and are cross-platform and may be designated by either the ".ttf" or ".otf" suffix. TrueType flavored OTFs are thus backwards compatible on Windows operating systems as long as they are designated with the ".ttf" suffix. However, TrueType fonts do not appear with the OpenType icon unless they are digitally signed by the font foundry.