It's referenced in the Registry in HKEY_LOCAL_MACHINE\SOFTWARE\TRADOS\Shared\Plugins\FileFilters
However, you shouldn't need to go there. If you go to your install folder (by default: C:\Program Files (x86)\SDL International\T2007\TT\) you'll find a FilterDefinitionFile.reg file.
If you run this file it will set this registry to the path referenced in this reg file. This is based on your system and is created dynamically during installation.
To check where it's pointing to, you can open this file in Notepad.
It needed to be registered by FilterDefinitionFile.reg.
Thank you very much Luis and best wishes!