We frequently send STEP files of our product to clients. Up until recently we would just make a STEP file of the SW assembly, but we would rather send 'immobilized' STEPs in which the assembly can only be viewed as a whole and the individual parts cannot be extracted.
Some online searching led me to the following method:
1. Save assembly as (multibody) part.
2. Combine bodies.
3. Save as Step.