.doc - Word 97-2003 Document - The binary file format.
.docx - Word Document 2007 and higher versions - The default XML-based file format.
.docm - Word Macro-Enabled Document 2007 and higher versions - The XML-based and macro-enabled file format.
.txt - Plain Text - A document as a .txt file, the document loses all formatting.
A header is the top margin of each page, and a footer is the bottom margin of each page. Headers and footers are useful for including material that we want to appear on every page of a document such as your name, the title of the document, or page numbers.