The setting is entitled "Don't Open Anything", and for obvious reasons it defaults to "off". Apparently, it's in case a PDF crashes the program, and its helpful automatic "open last file" feature will cheerfully re-crash the program every time you try to open it, and this switch is here to break the deadlock.
There's a beautiful inelegance to this. I can't really explain why I find it so amusing. It's like everything that is unavoidably futile about software development rolled into a single, one-switch setting screen. It is an open concession that it is not possible to simply prevent the program from crashing, or to even give it error recovery to close a file and kick back to the file selector with an error. Given the fact that GoodReader was the only mobile PDF reader (including my Kindle) able to read The Old New Thing, I'd infer this is because PDF is Difficult and it is impossible to adequately test every pathological thing the format can throw at you. So this is to the programmer's credit, not his detriment: it's an open concession of pseudo-defeat, to at least open up an explicit workaround, but is there a better practical strategy, given the behavior of iOS?
I've migrated to DreamWidth. The original post is at http://kistaro.dreamwidth.org/462680.html. View comments at http://kistaro.dreamwidth.org/462680.html#comments ; go ahead and use OpenID to post your own.