With OpenSSL you can convert pfx to Apache compatible format with next commands:
openssl pkcs12 -in domain.pfx -clcerts -nokeys -out domain.cer
openssl pkcs12 -in domain.pfx -nocerts -nodes -out domain.key
First command extracts public key to domain.cer.
Second command extracts private key to domain.key.
Update your Apache configuration file with:
...
SSLEngine on
SSLCertificateFile /path/to/domain.cer
SSLCertificateKeyFile /path/to/domain.key
...