I read this article on ZDNet about Google pulling out of China because of security threats. What interested me was the evidence discovering that Google wasn't the only company being hacked in this way. There were several other top companies that were being hacked by sophisticated means originating in China.
I think somewhere along the way Adobe changed what the PDF was for. It was never intended as an interactive way of displaying documents or filling in forms. It was supposed to be a way to transfer, view and print documents as they were intended. This seems to have changed through the life of the format something I think could lead to the odd security vulnerability every now and again.
In the old days it was pretty simple avoiding viruses. If someone sent you a program by email or you were asked to download and execute a program you were most probably likely to pick up a computer virus somewhere along the lines. Avoiding these kind of attacks were pretty simple, but as technology progressed avoiding viruses has become a bit of a nightmare. One attack that really had me worried the first time I had heard about it was a vulnerability in the JPEG format that could cause a buffer overflow error on Microsoft OS's at the time. This meant basically viewing an image on a webpage could give you a a virus! A JPEG is not an executable file just as a PDF is not an executable file in all rights I the user should feel perfectly safe viewing these files on my machine and not have to worry about viruses.
The problem has also become two fold. Anti Virus software vendors appear to be releasing never ending updates and their programs appear to be coming more and more bloated as a response to virus and hacking exploitations. Looking at the disk activity on your machine you will probably notice that most of it is the work of your virus scanner. If you are unlucky to have your virus scanner setup incorrectly or have a program such as Windows Defender and a Virus Scanner installed at the same time these program will inevitably scan what each other are doing which can lead your machine to grind to a halt as I have found. I think the Operating System needs to make a change to accommodate the fact that a Virus Scanner will be running and that somehow this needs to address the issues with performance on machines and work in harmony with the OS. Long standing applications such as Adobe Reader need to stop introducing progress by bloating their software just as the very web browsers we use now a days have started to become more and more bloated (again). Applications should come with the minimum required and if you choose to use the other features, it should ask you if you want to use them when the need arises or when you install them. If your application is trying to do too much maybe you need a separate application?