New
#11
Like all programs, the update targets vulnerabilities that have come to light since the previous version was released. In many cases, the performance is also improved. As with all programs, the more popular and well-known it is, the more susceptible it is to vulnerabilities, which is why both Adobe and Foxit release new versions on a regular basis. The others also release updated versions from time to time, but since they are not specifically targeted in the same way as their more well-known cousins, there is less of a need for the updates (although, having said that, you should make a point of periodically checking if there is an update available).