That might be tricky. An encrypted file may have some properties a random file does not have in general.

No, unless the algorithm is broken.

Ciphertext indistiguishability[1] is a basic requirement for any encryption scheme. All modern ciphers are designed to make that hard.

[1] https://en.wikipedia.org/wiki/Distinguishing_attack

Yes, but you remove that attack vector simply by encrypting a random file instead.