STL to X_T conversion most likely represents conversion of 3D model for printing (.stl) to solid model format, in this case Parasolid one (.x_t). Such conversion should be doable in any 3D modeling tool with support of Parasolid formats as well as 3D printing. You can even find dedicated 3D model converters.
Open STL file Open X_T fileA set of 3D modeling tools
A CAD conversion software
A CAD visualizaton, analyzation and translating system
A dedicated CAD converter