What is p12 and pem file

Ans : 

p12 : .p12 is an alternate extension for what is generally referred to as a "PFX file", it's the combined format that holds the private key and certificate and is the format most modern signing utilities use. Same with alternate extensions are .PFX, .PKCS12 

pem : this is a container format that may include just the public certificate (such as with Apache installs, and CA certificate files /etc/ssl/certs), or may include an entire certificate chain including public key, private key, and root certificates. 

Convert from .p12 file to .pem file 

cdcd Desktop openssl pkcs12 -in pushcert.p12 -out pushcert.pem -nodes -clcerts