Man pages matching name gnutls_pcert_import_x509 in section 3:

gnutls_pcert_import_x509.3.en	debian 10 / gnutls-doc
gnutls_pcert_import_x509.3.en	debian 11 / gnutls-doc
gnutls_pcert_import_x509.3.en	debian 12 / gnutls-doc