diff --git a/lib/avatax/client.rb b/lib/avatax/client.rb
index d300800..4c11264 100644
--- a/lib/avatax/client.rb
+++ b/lib/avatax/client.rb
@@ -33,5 +33,6 @@ class Client < API
     include AvaTax::Client::Utilities
     include AvaTax::Client::ShippingVerification
     include AvaTax::Client::AgeVerification
+    include AvaTax::Client::MultiDocument
   end
 end