Newline characters are, for practical purposes, invisible. As the name implies, they are at the end of each line, and would be an equivalent of hitting the Enter/Return key on a keyboard, or pushing a lever on a typewriter to move the cylinder up by one line. Just like you don't see newline character in MS word when you type (unless you turn that particular function ON), they are invisible to the eye in most file types. In Linux, an ASCII character numbered 10 (0a hexadecimal) is the newline character, while under Windows it is actually two characters (10 + 13, or 0a + 0d).
I don't know why you would need to find them or remove them, since they are interpreted by most programs exactly as they should be.