If you are trying to export windows certificate with private key, and windows export wizard provides no such possibility (export with private key is grayed out) because private key has been install as non-exportable (what is the default when importing, what almost nobody changes), there is a great tool mimikatz that makes this possible.
Download it from http://blog.gentilkiwi.com/mimikatz.
And follow this procedure:
crypto::patchcngif previous did not work)
crypto::listCertificates) to list keys/certificates
crypto::exportKeys (or crypto::exportCertificates) to export what you want
That’s all. Exported keys will be protected with password ‘mimikatz‘ – you will need to enter it when importing certificate again.