It replaces the text editor of previous Macintosh operating systems, SimpleText. TextEdit reads and writes documents in Rich Text Format and Rich Text Format with attachments as well as plain text and HTML, and can open (but not save) old SimpleText files. It also has access to the operating system's built-in spell-checking service. The version included in Mac OS X 10.3 "Panther" added the ability to read and write documents in Microsoft Word format.
Formatted text, justification, and even the inclusion of graphics and other multimedia elements are supported by TextEdit, as well as its ability to read and write to different character encodings, including Unicode.