CorelDraw templates (.cdt) can only be used in the original program, so if you hope for a cdt conversion of any kind, you will need the software. Whenever cdt to plt conversion is actually possible could not be reliably verified. However, considering CorelDraw allows export to HP plotter graphics (.plt), it should be doable.
Convert CorelDRAW template file to HP Graphics Language plotter file.
We have found 2 software records in our database eligible for .cdt to .plt file format conversion.
Microsoft Windows software - convert cdt to plt on Windows
A set of applications used by professional graphic designers
Convert from cdt file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned cdt to plt. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Multiplatform software - convert cdt to plt on any platform
A vector graphics editor