All sorts of data can be encrypted by using the PGP program. This includes text, number and other data including pictures. Since the message is coded, it is difficult to break open the message and be accessed by a person other than its intended recipient.
A method used in the PGP program is called the holding 'key'. In this method the message in plain text is encrypted and converted into ciphertext and then converted back to plain text once it reaches the recipient, thus enabling the latter to read the message without any problem.
While encrypting the message two keys are used. The 'public key' is published far and wide and can be seen by anyone, but the 'private' key' of the message is not disclosed. The recipient of the message only can access the private key, when the message is decoded into plain text.
The message, which is encrypted through the private key, is only accessed by the recipient, and only the recipient knows how to decrypt the message. In all other forms of encrypting, the message can be decoded by an unauthorized person and read, but since in PGP the two different keys are used to protect its privacy, it can never be broken or decoded and the process is much safer than other methods of secure communication.
There is no way to access the private key of message in the PGP program, unless the person who is authorized to access the message or the person who encrypts the message reveals to an unauthorized person.
The trust factor is very important to ensure such communication. Since most of the communication that takes place in the form of encrypted messages is classified it is essential to involve only the people who are trusted in the process.