Interesting question. I guess it all depends on how much he jumps around between files and different parts of files.
There's a scene in Cryptonomicon by Neal Stephenson which is similar to this problem. The protagonist is in jail with a laptop which has the location of treasure on it encrypted by a WWII Enigma machine. However, the bad guys can see his screen at all times, so he needs to write the code to crack the cipher without looking at the data. I won't spoil how he does it because I recommend reading the book.
There's a scene in Cryptonomicon by Neal Stephenson which is similar to this problem. The protagonist is in jail with a laptop which has the location of treasure on it encrypted by a WWII Enigma machine. However, the bad guys can see his screen at all times, so he needs to write the code to crack the cipher without looking at the data. I won't spoil how he does it because I recommend reading the book.