stp to x_b conversion essentially means export of 3D models saved in ISO STEP product data files (.stp, .step) to one of the formats used by Parasolid (.x_b). It should be doable in several CAD programs or even some of the dedicated 3D modeling / conversion software.
Open STP file Open X_B fileA 3D product data optimalization software
A CAD conversion software
A CAD visualizaton, analyzation and translating system
A dedicated CAD converter