Convert IPJ to STP

ipj to stp conversion is most likely related to export of Autodesk Inventor projects (.ipj files) to one STEP product format (.stp, .step), something that is certainly possible with Inventor itself. It is unlikely this works for whole assemblies, so in case of these you will have to disassembly the object and export individual parts. You can even find some 3D model converters for this.