Decrypting an already sent encrypted file in PGP I am a novice in cryptography and need few clarifications.

If I am SenderA, sending document to Receiver using PGP encryption. Let's say, SenderA shuts down and SenderC takes on the role of SenderA. SenderC gets hold of the secret key from SenderA (to minimize disruptions of adding new keys and involving Receiver).

If I only have list of encrypted files that SenderA sent earlier, how can I as a SenderC decrypts those files back into original? 

Any help will be much appreciated.
When encrypting with PGP, it's common for the sender to add themselves as a recipient. When they do that, they are able to decrypt their own messages at a later time.

If the sender doesn't do that, they simply won't be able to decrypt their previously sent messages.