Of course you can hide the existence of the message. The art and science of doing so is called steganography. Some forms of steganography are intended to be completely undetectable, while others merely offer plausible deniability.
> Generally though, there are many techniques known to be able to hide messages in data using steganographic techniques. None are, by definition, obvious when users employ standard applications, but some can be detected by specialist tools. Others, however, are resistant to detection - or rather it is not possible to reliably distinguish data containing a hidden message from data containing just noise -
You cant hide the existence of the data. You can pretend that it's just random bits. But they are still here, and an opponent can see them.
https://en.wikipedia.org/wiki/Steganography