The full form of PDF is "Portable Document Format". It is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. PDF files can contain links and buttons, form fields, audio, video, and business logic, and can be signed electronically. They are useful for preserving the original formatting of a document, sending a document electronically while ensuring that the recipient sees it exactly as the sender intended it to look, and creating a document that cannot be easily edited. PDF files are also portable, meaning they can be opened on any operating system, making them easy to share and store.