可以考虑使用逐步解密的方法，以减少内存的使用。下面是一个代码示例：

using System.IO;
using System.Security.Cryptography;

public static void Run(Stream pgpEncryptedStream, Stream pgpPublicKeyStream, ILogger log)
{    
    // Get the PGP encrypted data from the input stream
    var pgpEncryptedData = ReadFromStream(pgpEncryptedStream);

    // Get the PGP public key from the input stream
    var pgpPublicKey = ReadFromStream(pgpPublicKeyStream);

    // Load the PGP public key
    using var publicKeyStream = new MemoryStream(pgpPublicKey);
    using var publicKey = new PgpPublicKeyRing(publicKeyStream).GetPublicKey();

    // Create a PGP encrypted data stream
    using var pgpEncryptedDataStream = new MemoryStream(pgpEncryptedData);

    // Create a PGP decryptor
    var decryptor = new PgpDecryptor(pgpEncryptedDataStream, publicKey);

    // Create a buffer for the decrypted data
    var buffer = new byte[4096];
    var output = new MemoryStream();

    // Read the decrypted data into the buffer
    var decrypted = 0;
    while ((decrypted = decryptor.Read(buffer, 0, buffer.Length)) > 0)
    {
        output.Write(buffer, 0, decrypted);
    }

    // Set the position of the output stream to the beginning
    output.Position = 0;

    // Do something with the decrypted data ...
}

// Helper method to read data from a stream
private static byte[] ReadFromStream(Stream stream)
{
    using var memoryStream = new MemoryStream();
    stream.CopyTo(memoryStream);
    return memoryStream.ToArray();
}

在此示例中，我们使用了逐步解密的方法，以便降低内存使用量。我们首先将PGP加密数据和公钥加载到内存中。然后，我们创建一个PgpDecryptor对象，并在循环中读取加密数据。我们使用一个缓冲区来存储解密的数据，并将其写入一个MemoryStream中，以便我们