.txt extension suggest me a dictionary attack.
using the bip39 wordlist, there are a total of 161,735,049,399,563,309,103,078 valid possibilities to try.
this number was derived using the following algorithm:
for each combination with repetition of the set 3..8 of length 8:
skip if 32 != sum of set of current combination
for each permutation without duplication:
size += product(size(number of words of length x for each element of the current combination))