AES implementation to encrypt files
To make the encrypt and decrypt passwords different, whoever has access to the encryption password would also need to know the key derived from the decrypt password, and the encrypt password simply unlocks that key. Then you have something like this:

Enc password is entered
Enc password is derived to key $K_E$
$K_E$ is used to decrypt the stored decrypt key $K_D$
A random key $K_R$ is used to encrypt the data
$K_R$ is encrypted with $K_D$ and appended to the message with the IV

Upon decrypt, the correct password will be derived to $K_D$ and used to unlock $K_R$, which can then decrypt the message.

In regards to the rest of your system, reading line by line is a very bad idea. In this case you are not encrypting the line breaks, and someone looking at the encrypted data will know the approximate structure of the message. You should read the file as a stream of bytes from end to end and encrypt all of them. The ciphertext should also not use any kind of encoding, as that could cause a problem during decryption. If you need the ciphertext to be copyable as text, like into an email or text message, it should be encoded to Base64.

Also simply hashing a password for use as a key is wrong, you need a key derivation function such as PBKDF2. There are MANY questions regarding this here, I would suggest reading a few of the highest voted questions and answers.