There is only one file type that uses the .PAGES-TEF extension:
Pages iCloud Document
Text document created by Pages, the word processor included with Apple's iWork suite; used as the save format when a user chooses to save the document to iCloud; differs from the standard .PAGES extension, but doesn't affect the contents of the document when reopened in Pages.
NOTE: Numbers spreadsheets in iCloud use the .NUMBERS-TEF extension, and Keynote iCloud presentations use the .KEY-TEF extension.
Updated: January 10, 2016