If you have created the .PFX file from Windows Certificate Services. Suppose to use with Apache in Linux server, can convert PFX to .key and .cer certificate because of The PFX contains the entire certificate chain. 

Using OpenSSL command we can convert pfx to Apache compatible format, the commands are,

# openssl pkcs12 -in yourdomain.pfx -clcerts -nokeys -out yourdomain.cer

# openssl pkcs12 -in yourdomain.pfx -nocerts -nodes  -out yourdomain.key   

The 1st command convert to .cer format and 2nd  convert to .key format.

Once updated these file format update in your configure file apache2.conf or httpd.conf,

 SSLEngine on
 SSLCertificateFile /path/to/yourdomain.cer
 SSLCertificateKeyFile /path/to/yourdomain.key

Finally restart the apache service,

# service apache2 restart