Render paragraph reference field in page.html.twig
but if I add an extra field to the paragraph type, it is not updated.
  I would like to render all fields, even if I add a new field in the
  future.


To answer the question, you just need to loop though the paragraph fields. 

{% for item in node.field_intro %}
  {% for paragraph_field in item.entity %}
     {% if 'field_' in paragraph_field %}
       {{ paragraph_field.value }}
     {% endif %}
  {% endfor %}
{% endfor %}