In recent windows versions, open Windows Explorer - usually from Start-Programs-Accessories.
Click on any Folder
Select Tools from the bar at the top
Select the Folder Options Tab
Select the File Types Tab

This will show you all the "registered" file types, and what program is set to open them. Find your .crd and select it, then use the "change" button to associate it with a different file.

The .crd extension has been used for a number of different kinds of files, several of which were obsolete "mini database" things, where everything was stored in hex - so it comes out as mostly "unprintables." This doesn't sound like what you're getting, but I don't know what current file types use that extension.

John