If you used another tool, such as OpenSSL, to obtain the NSX Manager certificate, make sure the certificate and private key are in the PKCS#12 format. If your NSX Manager certificate and private key are not in PKCS#12 format, you must convert them before you can import them into NSX Manager.
Verify that OpenSSL is installed on the system. You can download openssl from http://www.openssl.org.
openssl pkcs12 -export -out server.p12 -inkey server.key -in server.crt -certfile CACert.crt
In this example, CACert.crt is the name of the root certificate that was returned by the certificate authority.
What to do next
Import the signed SSL certificate into NSX Manager.