CDT files are so-called CorelDRAW Image Templates, so picture templates for CorelDraw. CorelDraw is a vector graphics program that is part of CorelDraw GraphicsSuite.
CDT files contain information about properties for new images, such as fixed graphics and objects, fill and gradient settings, and document settings such as dimensions and rasters.
It should be noted that template files from newer versions of the program can not usually be imported into older versions and versions X4 and X5 are only backward compatible with files up to version 7. InkScape supports versions V7 to X3.
Most often resolving problems with opening CDT files is very simple. Just install an appropriate program that supports such files. All of the listed programs support CDT files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of CDT files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate CDT files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Inkscape applications is not on the list, select "Browse" option in order to manually locate the directory where Inkscape has been installed.
Sometimes problems with opening CDT files may not lie with the application itself, but can arise due to other causes, such as: