In a multibody part, you can combine multiple solid bodies to create a single-bodied part or another multibody part.
You can add or subtract bodies, or keep material that is common to the selected bodies.
You can only combine bodies contained within one multibody part file. You cannot combine two separate parts. However, you can create a multibody part by using Insert Part to place one part into the other part file. Then you can use Combine on the multibody part.
It is strongly recommended that you do not use the Combine feature to combine weldment bodies. It is not always possible to calculate the cut list properties accurately for a body created using the combine feature.