A LaserJet Pro 400 driver enables a computer to send out properly-formatted information so text and images can be printed by a LaserJet Pro 400. Without this driver, the LaserJet Pro 400 loses all printing functionality.
Most software for which the ability to print is a major feature faces the challenge of interfacing with a variety of different printing devices. Microsoft Word, for example, has its own internal file format, which is coded differently from information that might be recognized by a LaserJet Pro 400, which is in turn coded differently from information recognized by other printers. Rather than each piece of software having a sprawling block of extra programming to help translate its information into a language understood by hundreds of different printers, a printer driver acts as a single bridge carrying information from the computer it is installed on to the specific printer it is designed to work with.
Modern operating systems such as Windows 10 tend to automatically detect and install device drivers when new hardware is plugged in. However, printer drivers are often updated over time to fix bugs and streamline the device's functionality. Hewlett Packard, manufacturer of the LaserJet Pro 400, allows the latest version of the printer's driver to be downloaded from the HP Support Center website.