FRC was the thing I immediately thought about when I saw this (they still do PDF encryption), but the techniques here don't really apply. I'm pretty sure that

FRC was the thing I immediately thought about when I saw this (they still do PDF encryption), but the techniques here don't really apply. I'm pretty sure that you could just try to brute force it, as the passwords as usually dictionary-based with substitutions (e.g. R0bot$InSp&ce). Edit: After taking a much more in-depth look at it, all of the past game manuals' passwords are too complex to crack in a reasonable time (even with a dictionary). With a top 1000 word list dictionary with substitutions of 3-letter words like the above there are (conservatively) 1x10^20 combinations. You can't crack the PDF user key directly either, because recent game manuals use 256-bit AES keys.