Reverse engineering is primarily used for:

Concept

Reverse engineering is the process of analysing an existing system, component, or piece of software — working backward from the finished artifact — to recover its structure, behaviour, and design, without access to the original blueprints. Its core purpose is comprehension and documentation, not creation.

Application

Applied to software, an engineer inspects, decompiles, or traces an existing, often undocumented, program to recover its architecture, algorithms, and data structures, and then records those findings. That activity is exactly what the correct option describes: understanding and documenting existing software.

Cross-check

• Creating new software from scratch describes forward engineering — building a new system from requirements — the opposite direction from analysing something that already exists.

• Improving software performance describes optimisation or tuning, a separate activity aimed at speed or resource efficiency, not at recovering design knowledge from an existing system.

• Testing software components describes quality assurance — checking behaviour against a specification — not working backward to discover unknown design information.