A file viewer is 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.
File viewers do not edit files, yet it is common for them to be able to save data in a different file format, or to copy information from the viewed file to the system-wide clipboard.
File viewers have to have sufficient knowledge about the format of the file to be viewed. Even plain text files are not so simple — file viewers may have to handle different code pages and newline styles.
A fundamental type of file viewer are 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. Disassemblers also fall in this category.
Another common type of file viewer is a picture viewer that can display picture files of various formats. Common features here are 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 may be distributed free of charge, while editors have to be bought).
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.
The primary reason behind this missing functionality is often due to marketing and control. For example, a popular software program, Adobe Acrobat, can be used to create 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 program, the Acrobat Reader, and made it available for free. This viewer application allows the content created by the proprietary authoring software to be readable on all supported operating-system platforms, free of charge, thus making it a more attractive solution.
There are many products that can qualify as a file viewer: Microsoft Word viewer or Microsoft PowerPoint viewer, and the OpenOffice equivalents are examples. In a sense, a web browser is a type of file viewer, which translates, or renders, the HTML markups into a human-friendly presentation. Although HTML is plain text, viewing an HTML file in a browser and in a text editor produces significantly different results.
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