PDF is a file format developed by Adobe Systems for representing documents in a manner that is separate from the original operating system, application or hardware from where it was originally created. A PDF file can be any length, contain any number of fonts and images and is designed to enable the creation and transfer of printer-ready output.
Each PDF file encapsulates a complete description of a 2D document (and, with the advent of Acrobat 3D, embedded 3D documents) that includes the text, fonts, images and 2D vector graphics that compose the document. They do not encode information that is specific to the application software, hardware, or operating system used to create or view the document.
The .oeb file extension was created for use in accordance with the Open eBook Standard which was overseen by the Independent Digital Publishing Forum (IDPF). This is now a legacy format, having been superseded by the epub file type.
Based on XML, the oeb file defines how multiple sources should be ordered and arranged into a single electronic delivery for the user to consume. This means that there Is one file to be transferred between the vendor and customer rather than multiple files. The file type permits the use of DRM protection. The format was designed to be open and easily used by any online bookstore.