var storedProcedureUri = UriFactory.CreateStoredProcedureUri("MyDB", "MyCol", "MyProc");
var requestOptions = new RequestOptions { PartitionKey = new PartitionKey(myPartitionKey) };
var procedureResponse = await Client.ExecuteStoredProcedureAsync<MyObjType>(storedProcedureUri, requestOptions);
var document = procedureResponse.Response;

return document;