just to comment on doing booleans with licensed models. this is completely possible, as Suchit says. Sometimes I think users get confused by the lock symbols shown in the model. These locks are not related to the license protection at all, they are there because the model is posable and modifying individual parts would break the posability.
For you I would suggest to download the shell (surface enclosing the complete model) of DUKE and do the boolean operation with the shell only. For Duke you could use: https://itis.swiss/virtual-population/virtual-population/vip2/duke/duke-whole-body-shell-v2-0/
Since the shell is not license protected you can modify it, save it as STL or whatever format and load it other software tools if needed (e.g. MATLAB). To make it a solid the easiest method is to import the STL file and check the box "Import as Solid".
We are planning to restructure the downloads soon, and I want to add the shell surface by default to the zip file containing the full V3.x model, since it is often useful, e.g. to create uniform thickness offset surfaces (skin layers), and other operations.