You can use cut
:
cut -c N- file.txt > new_file.txt
-c:
characters
file.txt:
input file
new_file.txt:
output file
N-:
Characters from N to end to be cut and output to the new file.
Can also have other args like: 'N' , 'N-M', '-M' meaning nth character, nth to mth character, first to mth character respectively.
This will perform the operation to each line of the input file.