Help how to open CTD files:
To use/open/view the file, try to use suggested associated applications (if available). If not, try to use any plain text editor like Notepad under Windows, TextEdit under MAC OS X, or some of more advanced simple text or source code editors like Notepad++, PSPad, Programmer's Notepad, UltraEdit that are capable to view and correctly read text files also writed at different platforms (Windows, MAC or UNIX format) and character sets (UTF-8, ANSI, Windows charsets, Cyrillique, Arabic and other foreign languages text encoding charsets etc.) and also with additional source code formatting capabilities.
How to convert file with extension CTD:
If your opened file type is simple text file, you don't need to converting it. You can rename file extension to .txt or text file extension you currently need for your associated program or project. There can be sometimes problems with right character encoding recognition and determining of used charset for text in the file and consequently converting into character set you want. Look for some text encoding converter software if your text editor can't convert text into code charset you need.
If your file is not simple text file (viewed text is corrupted, contains unknown symbols, special characters or binary code), you will need to find native text editor or word processing program for this file type or similar program capable to import this text file format. Try to do some internet search for the right application for this file type.
.
.
SourceForge.net