1. Install OpenSSL version 0.9.8 for windows, you can get it from below link:
http://slproweb.com/download/Win32OpenSSL_Light-0_9_8zb.exe
2. Install it on a windows machine. By default, OpenSSL will be installed to C:OpenSSL
3. Copy the pfx certificates into folder C:OpenSSLbin
4. Run command line as administrator, and go to folder C:OpenSSLBin
5. Use below command to covert the certificate:
a. Generate crypt key file for the certificate via below command:

openssl pkcs12 -in server.pfx -nocerts -out server_tmp.key 

During this step, it will ask for pfx certificate password and the pass phrase for the key. Use any word you like as the pass phrase, do not use blank pass phrase.
Then use below command to decrypt the key. In this step it will ask you the pass phase you used before.

openssl rsa -in server_tmp.key  -out server.key

b. Generate crt file for the certificate via below command:

openssl pkcs12 -in server.infau.wbcau.westpac.com.au.pfx -clcerts -nokeys -out server.crt 

6. Done. Now you can install the certificate for ESXi host