from the Crypt::OpenPGP manual...

$pgp->encrypt (%args)

%args can contain: 
* Data  - The plaintext to be encrypted. This should be a simple scala
+r containing an arbitrary amount of data. 

Data is optional; if unspecified, you should specify a filename (see F
+ilename, below).
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So you should just be able to call

$pgp->encrypt(Data=>$credit_card_number,Recipients=>$key_id,Armour => 
+1,);
[download]

Cheers,
Ben