I just upgraded to CorelDraw 2018. In this new version .CDR file doesn't open with double click from the folder. It opens Corel program every time but not the file.
.CDR files only open from the File menu or by dragging from the folder.
You'll need to uninstall the old Corel Graphics - Windows Shell Extension, make sure the versions match. If they do not match, uninstall both and reinstall Windows Shell Extension.
Example location: C:\Program Files\Corel\CorelDRAW Graphics Suite 2018\Setup\MSIs
File Name: ShellExt.exe
This would also fix any other issues like thumbnails not previewing etc.
I have never found a fix for this on the net, but I stumbled across a solution by chance! Double click the cdr file and an empty CorelDraw instance opens. Leave this window running. Click the cdr file and 'Open With' CorelDraw. It then appears in the empty instance. Close CorelDraw. Then double click the cdr file and this time it opens in CorelDraw! The same goes for CorelPaint, by the way.