fbx to x_t conversion is often used as means to transfer 3D content between different 3D model / CAD design solutions and FBX format is used for it's interoperability and is supported in pretty much every modern software, either natively or via plugins.
If you do not have access to Parasolid software, your only remaining options is to use one of the dedicated CAD/3D model converters, for example the popular CAD Exchanger.