alt Hacker News> PDFs are executables, that's why it's hard.
That isn’t really true, it’s not hard for PDF viewers to block by default (or just not implement) the problematic features, which also aren’t critical for the vast majority of PDF files.
The exploitable bugs are typically the usual, some buffer overflow in an underlying image or font library or similar, but unrelated to PDFs being “executable”.
What a sleight of hand. PDF's are obviously not executable, any more than text files are. Decoders are executable and they can choose to unsafely handle input. Even plain text editors can have exploits. It's no different than any piece of complex software.