If a third party is encrypting files before transferring them to you, they should encrypt the files to your public key. You can then decrypt the files using PGP Zip which is included in PGP Desktop (Symantec Encryption Desktop).
If there is a high volume of files and a team of users need to be able to decrypt the files, the third party can encrypt the files to the public keys of all users in the team.
However, the third party may only be willing or able to encrypt files to a single public key.
In this scenario, you can create a custom key for the third party to use. In order to be able to decrypt the files, each member of the team will need to import the custom private key (key pair) to their Encryption Desktop local keyring.
There are three methods of accomplishing this: