Files with cdn file extension can be found as CD labels made in Click'N Design 3D software.
CDN file extension - Click'N Design 3D CD label
What is cdn file? How to open cdn files?
File type specification:
The cdn file extension is used for cd labels created with the use of older Click'n Design 3D software.
Although still available for download on some sites, it looks like the program is no longer supported.
This cdn file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.