Follow this translated answer from another question from SO en :

What is the difference between a cer, pvk, and pfx file?

  

Windows uses the .cer extension for an X.509 certificate. These can   be in "binary" ( ASN.1 DER ), or it can be encoded with Base-64 and have   an applied header and footer ( PEM ). Windows will recognize it as well.   To verify the integrity of a certificate, you must verify   your signature using the issuer's public key ... which is, for your   another certificate.

     

Windows uses .pfx for a PKCS # 12 file. This file may contain   a variety of cryptographic information, including certificates,   certificate chains, root authority certificates, and keys   individuals. Its content can be protected cryptographically (with   passwords) to keep the private keys private and preserve the   integrity of root certificates.

     

Windows uses .pvk for a private key file. I do not have   sure that standard (if any) Windows goes into these. We hope   are coded PKCS # 8 keys.

     

You should never reveal your private key. These are contained in    .pfx and .pvk files.

     

Generally, you only trade your certificate ( .cer ) and the certificate   intermediary issuers (ie the certificates of all   your CA's , except CA root) with other parts.