Several file types use crd extension and it is likely that at least some of them can be exported as PDF document. This can be typically achieved with a program that can open/view them and also has either native PDF export function, or at least allows printing in which case you can use a virtual PDF printer to achieve crd to pdf conversion.
Nevertheless, a lot of users also look for a way to export CorelDraw graphics (.cdr) as PDF documents, something which is covered under cdr to pdf conversion.
Open CRD file Open PDF file