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.