File viewer
A file viewer is an application software that presents the data stored in a computer file in a human-friendly form. The file contents are generally displayed on the screen, or they may be printed. Also, they may be read aloud using speech synthesis.
Overview
File viewers do not edit files, yet it is common for them to be able to export data in a different file format, or to copy information from the viewed to the system-wide clipboard. A file viewer is limited-functionality software in the 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.
File viewers have to have sufficient knowledge about the file format to be viewed in order to handle different byte orders, code pages or newline styles.
Some file viewer may be classified as filters that translate binary files into plain text (one example antiword). However, depending on the competence of the translating routines, some information may be lost.
Image viewers display graphics files onscreen. Most viewers are capable of reading multiple graphics file formats but some such as JPEGview are dedicated to a single format. Common image viewer features include thumbnail preview and creation, and image zooming.
For more complex or proprietary file formats, file viewers are usually provided by the same companies that make the editing software using those formats. Viewers are usually distributed free of charge, while editors have to be bought. For example, the full version of Adobe Acrobat can be used to create content for most computer platforms. To ensure that people can access the documents created with Adobe Acrobat, the software publisher created a viewer program, the Acrobat Reader, and made it available for free. Microsoft also makes viewers for Word and PowerPoint documents freely available. These viewer applications allow the file format to be readable on all supported operating-systems, free of charge, making the commercial product a more attractive solution.
A web browser is a type of file viewer, which renders HTML markup into a human-friendly presentation. Although HTML is stored in plain text files, viewing an HTML file in a browser and in a text editor produces significantly different results. Web browsers may also be used to view image and multimedia files.
Streaming media
There are also types of data that are not intended for static display — these incorporate the time dimension. Viewers for such formats are named players. But the essence is the same — presenting file contents in human-friendly form (i.e. displaying video on the screen as intended, or playing sound through loudspeakers). And the same consideration of different file formats is present.