OpenType (OTF) is a scalable computer font format built on TrueType, developed jointly by Adobe and Microsoft. It extends the TrueType format by adding support for advanced typographic features such as ligatures, small caps, alternate characters, and multiple language scripts within a single file. OTF files are cross-platform and widely used in professional design and publishing. Sample OTF files are critical for testing advanced typography applications. Developers use them to verify that complex text layout engines (like HarfBuzz) correctly handle OpenType features. They are also used to test font subsetting for web performance and to validate cross-platform font portability between Windows, macOS, and Linux environments.