PDF in the context of Acrobat Reader

A markup language is a text-encoding system which specifies the structure and formatting of a document and potentially the relationships among its parts. Markup can control the display of a document or enrich its content to facilitate automated processing.

A markup language is a set of rules governing what markup information may be included in a document and how it is combined with the content of the document in a way to facilitate use by humans and computer programs. The idea and terminology evolved from the marking up of paper manuscripts (e.g., with revision instructions by editors), traditionally written with a red pen or blue pencil on authors' manuscripts.

An electronic document is a document that can be sent through non-physical means, such as telex, email, and the internet. Originally, any computer data were considered as something internal—the final data output was always on paper. However, the development of computer networks has made it so that in most cases it is much more convenient to distribute electronic documents than printed ones. The improvements in electronic visual display technologies made it possible to view documents on a screen instead of printing them (thus saving paper and the space required to store the printed copies). However, using electronic documents for the final presentation instead of paper has created the problem of multiple incompatible file formats. Even plain text computer files are not free from this problem—e.g. under MS-DOS, most programs could not work correctly with UNIX-style text files (see newline), and for non-English speakers, the different code pages always have been a source of trouble.

Even more problems are connected with complex file formats of various word processors, spreadsheets, and graphics software. To alleviate the problem, many software companies distribute free file viewers for their proprietary file formats (one example is Adobe's Acrobat Reader). The other solution is the development of standardized non-proprietary file formats (such as HTML and OpenDocument), and electronic documents for specialized uses have specialized formats—the specialized electronic articles in physics use TeX or PostScript.

DjVu is a computer file format designed primarily to store scanned documents, especially those containing a combination of text, line drawings, indexed color images, and photographs. It uses technologies such as image layer separation of text and background/images, progressive loading, arithmetic coding, and lossy compression for bitonal (monochrome) images. This allows high-quality, readable images to be stored in a minimum of space, so that they can be made available on the web.

DjVu has been promoted as providing smaller files than PDF for most scanned documents. The DjVu developers report that color magazine pages compress to 40–70 kB, black-and-white technical papers compress to 15–40 kB, and ancient manuscripts compress to around 100 kB; a satisfactory JPEG image typically requires 500 kB. Like PDF, DjVu can contain an OCR text layer, making it easy to perform copy and paste and text search operations.

The PDF Association promotes the adoption and use of International Standards related to PDF technology by assisting enterprise content management (ECM), document management system (DMS) and advanced PDF users with the implementation of PDF technology on an organizational level. In order to assist companies in making the most of PDF technology, the PDF Association provides organizations with information and resources on the variety of International Standards available for PDF.