Important assumptions are listed below:

$$ Assume that each $0$ or $1$ uses the space of one character.

$$ Assume that a single letter, $($such as A$),$ can be used to replace a pattern of zeros and ones and this letter also uses the space of one character.

$$ Assume the number of characters represents the size of the file.

$$ The mapping of a pattern to a letter $($ie $1101=$A$)$ is stored elsewhere. So any modified file will replace all repeated patterns with a letter $($A$).$