Allow custom fields on Print/Merge Document

(1) It's possible to define a set of custom fields for Print/Merge Document activities

(2) Then when you run a Print/Merge Document custom fields do not appear in the form

(3) If you view the activity created you can visualize the custom fields defined

As you can see there is an inconsistency between the defined behavior and the actual behavior. It would be really interesting to have this functionality fully developed. Could you, for example, allow you to search for all activities Print/Merge Document that meet the conditions of a custom field that defines the category of the document generated (certificate, letter, etc.)