The finetuning option ‘Maintain document types’ for activities is not visible in all cases.
You have to set the following scoping options in ‘integration into Sales, Service, and Marketing processes’.
The reason behind is that if you have a CRM integration it might be required to configure separate document types for the activities and map them accordingly in the codelist mapping.
This option is not available in C4C without integration in order to keep the configuration simple.
This might be changed in a future release- I will update the blog once this dependency has changed.