This was the content of the txt file :

There are some whitespaces in the text, some letters that comes more often than others (quick frequency analysis) => It must be a permutation.

Since the challenge is only worth 50 points (so probably meant to be easy), I figured it might just be a Caesar cipher. I tried a shift of 3 using the full ASCII table (0–127) as the alphabet.

I used this webapp : DCODE