Apple says they have successfully patched the PDF, this information right from Engadget.
JailbreakMe brought root to the iPhone 4-wielding masses, but also unearthed a nasty exploit in a PDF font. Thankfully for the rooted and those who never intended to root, Cupertino claims it has already patched the hole. "We're aware of the reported issue, we have already developed a fix and it will be available to customers in an upcoming software update," an Apple spokeswoman told CNET. We're not sure exactly when it will arrive, but we'd lay odds on soon -- in the meantime, don't open any PDFs you don't trust, don't do anything illegal or immoral, and hit up Comex's hack ASAP if your heart's still set on that shiny new unlock.