After disabling "Document ID Service" site collection feature, the field "Document ID" is still in the "Display Form". That's annoying.
However, it's easy to remove/hide it, with the help from the famous freeware "SharePoint Manager".
Go to the library, then expand "Fields", then change the property "Sealed" from True to False, click "Save"; then change the property "ShowInDisplayForm" from True to False, then click "Save" again.
PS: we cannot do the same change with this field in list content type or site content type.