A TDDD file is not a formal format and is generally just a program-defined file where the `. Here's more regarding TDDD file opener take a look at our own web site. tddd` tag acts as a label for whatever data the software stores—configs, serialized structures, or cache entries—making it usable only within that application; in gaming or simulation tools it may hold layout or scene details, and quite often the file is simply a renamed XML format or a binary file like SQLite that exposes its contents when opened in a viewer.