Man pages matching name coap-rd in section 5:

coap-rd.5.en	debian 10 / libcoap-1-0-bin
coap-rd.5.en	debian 10 / libcoap2-bin
coap-rd.5.en	debian 11 / libcoap2-bin
coap-rd.5.en	debian 12 / libcoap3-bin