I doubt it.
The prior two used PDF exploits in Safari.
While brilliant, I'm not sure if there are any exploits left.
There is, the reason being same as the problem. The code is so complex. PDF even supports its own scripting platform called Postscript. And to boot, we can edit these files on the computer, and we do not need to sign them to run them on the iPhone.
Imagine a reverse engineer, a hacker if you will. That has a working knowledge of how roughly PDF is built up, changing segments of the file while running the iPhone with a debugger in Xcode, at the same time even running a USB sniffer.
What he does, is that he wants the iPhone to crash, not all crashes are good enough, the type of crash most often used is called a buffer overflow, which some times allow to inject unsigned code right into play. If someone firstly gets a way of running unsigned code, it is only a matter of hours or days before a working jailbreak is in existence. It takes much longer now to package this, and even making sure its not dangerous to run. In worst case scenario, which is very often in fact, this is not enough to make an untethered jailbreak. But no problem if its just a PDF after you boot to get Cydia working it can be done every boot. But if we first can run unsigned code on the OS, its much easier to find a way to make the jailbreak unthethered. Sometimes it takes a while longer.
It has almost come to a point where it annoys me that people who does not understand that EVERYTHING is hackable, posts that "there are no more exploits now". Even the PS3 was said to be an unhackable fortress, though it just took some pissed of hacke(s) 3 weeks without Linux to run unsigned code. Even when exploits are fixed by updates, more features, and more exploitable code is put into the updates. So no need to worry
