Adobe Reader is one of the most popular programs on the Web. It's a free program that lets you easily view and sign PDF documents that anyone sends you. Since PDF documents are incredibly important, Reader is on most computers.
Hackers frequently target this program and so you need to install the frequent updates to keep hackers at bay. That's why I've rounded up links so you can make sure you have the most recent versions.
In order to download and use the updated versions, you must have a version of the program already installed. Adobe might also try to install Google Chrome and an Adobe toolbar as you're trying to update. Make sure you opt out of these if you don't want them.
No matter what you use, make sure you're running up-to-date security software, too. This will help prevent viruses from hitting your computer if hackers try to sneak one in.