You may be asking for steganography, where data is hidden in seemingly normal data/files. The hidden data can be encrypted or plaintext. There are many different applications of steganography, such as lists, text, images and file metadata.
Keeping entropy in encrypted data means insecure encryption. Think of rot13 or similar substitution ciphers where one character is always replaced by the same character. You have the same entropy in the ciphertext as in the plaintext but the plaintext is easily deduced from the ciphertext.
Good cryptographic algorithms depend on reliable pseudo-random number generators where every possible number has the same chance of appearing, but still leaving no clue as to which number is the next number. This results in high entropy so the plaintext is completely mumbled (very simplified explanation).
Note that hiding data (steganography) requires plenty of disk space since the wrapping data still needs to look "normal". Using image steganography also often results in noise or other effects that change the way the image looks.