3D PDF or eDrawings but make sure that the ability to measure is not selected when saving.
Any way you go they are going to be able to at least take measurements.
But they will not be able to see your design intent through seeing the features.
With all of that said you can save out your model as either an iges, parasolid,
or stp file. Another method is you could save out your part as one of the fore mentioned
methods and then reinsert that file into solidworks as a dumb solid then save that out as a part
file. All they would see in the feature manager would be an imported file that they can not extract.
Hope this helps. Good luck.
If it's an assy model, Save as a part with the Exterior Surfaces option.
You could also use the Defeature function.
Whenever we order models from subcontractors we get them as ACIS (.sat) files. This because we can use it for SolidWorks but also for our AutoCAD design team. It does the job that we can use the modelled part in our assemblies. However, if we want to change one thing we have to get back to the subcontractor (and pay them again of course ...).