To convert a .p7b certificate to a .pem certificate enter the following:
openssl pkcs7 -print_certs -in certificate.p7b -out certificate.pem
After this you can view the certificates with vi/less.
If you receive an error like below, you probably have a wrong format:
140536229615264:error:0906D06C:PEM routines:PEM_read_bio:no start line:pem_lib.c:703:Expecting: PKCS7
If the certificate in in DER format enter the following:
openssl pkcs7 -inform der -print_certs -in certificate.p7b -out certificate.pem