IETM (Interactive Electronic Technical Manual) is a digital manual that helps users understand and solve problems easily using interactive features. A PDF is also a digital manual, so it can be considered an IETM Level 2, but higher IETM levels are more advanced and user-friendly. Manuals are needed so users can refer to instructions and fix issues without always contacting the OEM or service center. As systems become bigger, the number of manuals also increases (user, operator, maintainer, spares, etc.), and it becomes difficult to refer to multiple hard copies or separate PDFs because they are not linked together. That’s why higher-level IETMs (Level 3 and Level 4) are useful—they work like a database where users can search quickly, jump to the right topic in seconds, and view related information easily.