xnview will display certain image files, like .cdr, in thumbnail view only.
You can tell which ones as they will have "{preview}" listed at the end of the file name like the example below:

If you have MS Office with the corel draw filter installed (cdrimp32.flt), you may be able to open the image and save it in another format using word,excel or pp via the Insert>Picture>From File menu.
See
this article for specifics and which versions of corel are supported.