"PFX" redirects here. For the managed concurrency library from Microsoft, see Parallel FX Library
The correct title of this article is PKCS #12. The substitution or omission of the # sign is because of technical restrictions.
In cryptography, PKCS #12 defines an archive file format for storing many cryptography objects as a single file. It is commonly used to bundle a private key with its X.509 certificate or to bundle all the members of a chain of trust.
A PKCS #12 file may be encrypted and signed. The internal storage containers, called "SafeBag"s, may also be encrypted and signed. A few SafeBags are predefined to store certificates, private keys and CRLs. Another SafeBag is provided to store any other data at individual implementer's choice. 
PKCS #12 is one of the family of standards called Public-Key Cryptography Standards (PKCS) published by RSA Laboratories.
The filename extension for PKCS #12 files is "
.p12" or "
These files can be created, parsed and read out with the OpenSSL
Relationship to PFX file format 
Actually PKCS #12 is the successor to Microsoft's "PFX". But confusingly the terms "PKCS #12 file" and "PFX file" are sometimes used interchangeably.  
Microsoft's "PFX" has received heavy criticism of being one of the most complex cryptographic protocols.
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