Force file extension to match file type

This policy setting controls how Excel 2007 loads file types that do not match their extension. Excel 2007 can load files with extensions that do not match the files' type. For example, if a comma-separated values (CSV) file named example.csv is renamed example.xls, Excel can properly load it as a CSV file.

If you enable this policy setting, you can choose from three options for working with files that have non-matching extensions:

- Allow different - Excel 2007 opens the files properly without warning users that the files have non-matching extensions. If users subsequently edit and save the files, Excel preserves both the true, underlying file format and the incorrect file extension.

- Allow different, but warn - Excel opens the files properly, but warns users about the file type mismatch. This option is the default configuration in Excel.

- Always match file type - Excel does not open any files that have non-matching extensions.

If you disable or do not configure this policy setting, if users attempt to open files with the wrong extension, Excel opens the file and displays a warning that the file type is not what Excel expected.

0. Allow different
   

   Registry Hive	HKEY_CURRENT_USER
   Registry Path	Software\Policies\Microsoft\Office\12.0\Excel\Security
   Value Name	ExtensionHardening
   Value Type	REG_DWORD
   Value	0

1. Allow different, but warn
   

   Registry Hive	HKEY_CURRENT_USER
   Registry Path	Software\Policies\Microsoft\Office\12.0\Excel\Security
   Value Name	ExtensionHardening
   Value Type	REG_DWORD
   Value	1

2. Always match file type
   

   Registry Hive	HKEY_CURRENT_USER
   Registry Path	Software\Policies\Microsoft\Office\12.0\Excel\Security
   Value Name	ExtensionHardening
   Value Type	REG_DWORD
   Value	2