CDR files are for CorelDraw products. CRD files that are created with CorelDraw versions 5-10 may open in Illustrator. CorelDraw versions 5-10 are quite old versions of CorelDraw. If you have CDR files that you want to use in Illustrator, you would need to open them in CorelDraw and then convert it to AI format. The Ai format will then be able to open in Illustrator.