Open it with edrawing and make it saved as and there you will see who is possible. If you get there, it is because he had checked the option and reverse.
I looked on the web and it seems that it is not possible to convert an EASM to a step. The EASM file is an exchange and intellectual protection file. So the simplest, ask your customer to provide you with a step of the assembly and if he can't ask for a bulky volume, for an integration it's enough
That's what it seemed to me. I tested this morning to open and register under to see if the STL option was enabled but it doesn't have it. As you say; you should see with your supplier for the sending of a WWTP.
As I said, ask your client for either a bulky volume, or a defeature or a speedpack . For the speedpack ask him to leave you certain face to be able to set constraints and possibly be able to control games, I have often used this method.