You must use the gpg command.
You can use the following to create portable public secret key pair.
gpg --export --armor [key] > my_gpg_pub-sec.asc
gpg --export-secret-keys --armor [key] >> my_gpg_pub-sec.asc
See man gpg for more information. The pub-sec ascii key file can be imported into gpg or other programs that are gpg compatible.