The purpose of MD5, and all the other “message hash” algorithms, is to be profoundly sensitive to any change, however slight. So, if you take a megabyte of information and change one solitary bit from 1 to 0 or vice-versa ... the hash won't be remotely the same as before.

Furthermore, you can't realistically devise a message, nor any change to it, that will yield any particular hash-value.

But the hash value that you obtain will always be the same size, no matter how much or how little (within reason...) information you hash.

The purpose of MD5, therefore, is not to be an “encryption” algorithm, but a “message integrity” algorithm. It is not reversible ... and it is designed not to be.