File extensions are a type of metadata appended to the end of computer file names to indicate to the operating system what format the file is in. It is by this mechanism that Windows knows to open File.txt with Notepad, File.doc with Microsoft Word, and to attempt to lauch File.exe as an application.
Changing the file extension on a file can render the operating system unable to open the file. Many modern operating systems hide file extensions from the end user by default for this very reason. Although in most instances changing file extensions is not recommended, there are situations where renaming power tricks can yield interesting results. From Word 2007 and forward, for example, Microsoft introduced the .docx format. The .docx format is essentially a .zip file filled with XML-based documents and the media embedded in the Word document. Armed with that knowledge, you could rapidly extract all the images embedded in a Word document by simply renaming File.docx to File.zip and opening up the document as you would a zip file.
- By Jason Fitzpatrick on 02/14/13