It's a great game. and to think they can make games like these even back in the pentium 4 era. I'll never be bored with games like this. just play it. get a walkthrough if you're stuck (seriously you'll need it)
make a new copy of Letter_23 and Letter_24, then rename them into Letter_437 and Letter_438 respectively. Also, Just in case do the same to Letter_23_R and 24_R. It worked for me at least.
https://youtu.be/-JIUHsvvhng