Write a program that turns every 17th bit of a text file to a 1
CJam, 22 bytes

q256b2H#b1f|2H#b256b:c


Try it online.

Touches every 17th bit, counting from the last.

I've used STDIN and STDOUT since CJam has no file I/O. If that's not allowed, the program can be wrapped in a Bash script at the cost of 24 extra bytes:

cjam &lt;(echo q256b2H#b1f\|2H#b256b:c)&lt;"$1"&gt;"$2"


How it works

q                      " Read from STDIN.                                                 ";
 256b                  " Convert to integer by considering the input a base 256 number.   ";
     2H#b              " Convert to array by considering the integer a base 2**17 number. ";
         1f|           " Set the LSB of every integer in the array element to 1.          ";
            2H#b       " Convert to integer by considering the array a base 2**17 number. ";
                256b   " Convert to array by considering the integer a base 256 number.   ";
                    :c " Turn character codes into characters.                            ";