PDF stands for "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 they can be signed electronically. They are primarily meant for viewing, not editing, and are useful for preserving the original formatting of a document. PDFs can be viewed on most devices using free software such as Adobe Reader. To save a file as a PDF, you can use the "Save As" function in most programs and select PDF as the file type.