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You received a STEP file from an engineer, a manufacturer, or a client. This is the international standard for exchanging 3D CAD data between different software — the one format that preserves geometry, colour, and assembly structure without being tied to any vendor.
STEP (Standard for the Exchange of Product Data) is an ISO standard (ISO 10303) maintained by a global committee rather than a company. It represents 3D models using precise mathematical surfaces (NURBS, B-splines) rather than triangle meshes, which means it preserves the engineering intent behind curved surfaces. This precision is why STEP is the standard for manufacturing — CNC machines and injection mould tools need exact geometry, not approximations.
FreeCAD (free, open-source) opens STEP files and can edit basic geometry. Fusion 360 (free for hobbyists) handles STEP natively. SolidWorks, NX, and CATIA all support STEP as an interchange format. For viewing without editing, CAD Assistant (free, from Open Cascade) displays STEP files on any platform. If someone asks you for a CAD file and you don't know their software, STEP is the professional choice.
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