A file viewer is a computer software that performs the translation of data stored in binary form to human-readable format.
Strictly speaking, file viewers translate files that are in a proprietary binary format instead of plain text. Nevertheless, this distinction between binary and plain text format is just a technicality, and mostly related to the default character-set of the given platform. Otherwise, even text files need to be translated from binary patterns into text, so to inspect any type of file a software is needed that can open the file and translate the binary pattern.
A file viewer is a limited-functionality software in a sense that it does not have a capability to create a file, or modify the content of an existing one. Instead, it is used only to display or print the content.
The primary reason behind this missing functionality is due to marketing considerations. For example, a popular software program, Adobe Acrobat, can be used to create a content for most computer platforms, under various operating systems. To ensure that people can access the documents created with Adobe Acrobat the software publisher created a viewer software, the Acrobat Reader, and made it available for free. This viewer software ensures that people can create content that is readable on all supported platform, free of charge, thus making it a more attractive solution.
There are many products that can qualify as a file viewer: Microsoft Word or Microsoft PowerPoint viewer are additional examples. In a sense, a Web browser is a type of file viewer, which translates, or renders, the HTML markups. Although HTML is plain text, viewing an HTML file in a browser or in a text editor can produce significantly different result.
Although web browser are undeniably the best file viewer, since they support many graphic, multimedia and document formats, they are still lacking the output quality and the performance of today's leading software packages such as Microsoft PowerPoint or Adobe Acrobat, so creating and using alternative publishing systems and accompanying file viewers still make a lot of business sense.