An installer is a small application you will download before installing a program. When you run it, it will begin the installation process of the program.
All the files you need to use the program used to be located on the discs that would come with applications you purchased in stores. Modern software will use an installer to look for those files online and download them for your convenience. This way you can choose to use a disc or you can download the application online like we do with Soda PDF.
Most installers will provide you some basic information about the program including access to some key settings.
Click here to learn more about downloading and installing Soda PDF.