How to convert .pem to .pfx?

i am working push notifications .i downloaded all required certificate csr and ssl certificates all things and also converting .pem format my webservices team providing services in asp.net so now we need to convert .pem format to .pfx format.how can we do this thing i am using following commands and links. but it is not working for me

openssl pkcs12 -export -in Certificates.cer -inkey key.pem -out Certificates.pfx -certfile CA.cer

And i was follow these link also but i got error.

http://ift.tt/1rQWKsb

i have these files

Certificate.p12 key.p12

Certificates.pem key.pem

ck.pem

Certificates.cer