.NUMBERS-TEF File Extension
File TypeNumbers iCloud Document
This file is saved in a binary format, which requires a specific program to read its contents.
What is a NUMBERS-TEF file?
Spreadsheet file created by Numbers, Apple's spreadsheet program included in the iWork suite; used as the save format when the user chooses to save the spreadsheet to iCloud.
Even though iCloud uses the NUMBERS-TEF extension, it shouldn't be an issue for users. When you open a spreadsheet on your Mac OS X or iOS version of Numbers, the spreadsheet will still load properly.
NOTE: Numbers spreadsheets saved on the local computer use the .NUMBERS extension.