Secure distribution of a confidential message can be performed by:
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Encrypting the message with the receiver's public key
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Encrypting a hash of the message
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Having the message authenticated by a certificate authority
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Using a password-protected file format
Public key encryption allows anyone to encrypt with the receiver's public key, but only the receiver with the matching private key can decrypt. This ensures confidentiality during transmission. The sender does not need to share a secret key with the receiver beforehand.
Encrypting a message with the receiver's public key ensures that only the holder of the matching private key can decrypt it, guaranteeing confidentiality during distribution — this is the core purpose of public-key (asymmetric) encryption. Hashing the message or having it certified by a CA addresses integrity or authenticity, not secrecy, and a password-protected file format is generally far weaker than proper public-key cryptography.