The Portable Document Format (PDF) is an open file format developed by Adobe in the 1990s to present documents, including text formatting and images. Hypertext Markup Language (HTML) is the standard markup language for creating web pages and web applications. Plain text is used for much e-mail. Electronic Mail Format (EML) for electronic mail or email, is a file extension for an email message saved to a file in the Internet Message Format protocol for electronic mail messages.