I been doing research on this matter cause I would like to live in Spain. I was Born in Puerto Rico and currently reside in Mass, USA. The Puerto Rican citizenship certificate is what you will need you have to apply thru the Department of state of PR.
you will need the following:
https://www.estado.pr.gov/en/certifi...g-regulations/
FORM: http://app.estado.gobierno.pr/formularios/CPR001.pdf (cant find it just google it "Puerto Rico CPR001" or "departamento de estado Cpr001").
Spain actually sees it as a legit document.

Also call consulate and ask for more information.