How to convert Siemens NX
to OBJ?

Siemens NX

A PRT file is a model part file saved in a three-dimensional model format used by Unigraphics, a 3D CAD program. It contains surface and solid information for a single part. PRT files are saved in a binary format, similar to an Alias wire model and an SDRC (Structural Dynamics Research Corporation) model.

OBJ

OBJ (or .OBJ) is a geometry definition file format first developed by Wavefront Technologies for its Advanced Visualizer animation package. The file has been adopted by many 3D graphics application vendors.

The OBJ file format is a simple data-format that represents 3D geometry alone — namely, the position of each vertex, the UV position of each texture coordinate vertex, vertex normals, and the faces that make each polygon defined as a list of vertices, and texture vertices. Vertices are stored in a counter-clockwise order by default, making explicit declaration of face normals unnecessary. OBJ coordinates have no units, but OBJ files can contain scale information in a human readable comment line.