Please note that "file://path/to/file.pem" in documentation means file protocol + file path. In UNIX like OS, that is something like file:///rsa_private_key.pem. There is THREE slashes in the path string, not TWO.
(PHP 4 >= 4.2.0, PHP 5)
openssl_pkey_get_private — Get a private key
openssl_get_privatekey() parses key and prepares it for use by other functions.
key can be one of the following:
The optional parameter passphrase must be used if the specified key is encrypted (protected by a passphrase).
Returns a positive key resource identifier on success, or FALSE on error.