Hi @David_Koth welcome to the community!
DocumentDB is not a MongoDB product but rather a re-implementation of an old MongoDB version with notable differences with the genuine MongoDB of similar version. Please see their documentation for more on this subject.
Thus using any MongoDB official tools on it is not supported. Even if mongorestore works, I would be suspicious if it doesn’t complain about something, as there are too many differences between it and a genuine MongoDB server.
If you need a cloud-hosted database and you’re not locked into a DocumentDB solution, I would encourage you to have a look at MongoDB Atlas, as this is created and supported by MongoDB. You would be able to use the official tools that you’re familiar with 
Best regards
Kevin