Corel draw 12 either is not importable using the selected filter, or this format is not supported

The culprit for the problem could be one of the following possibilities.

It's very likely the CDR file was saved in a newer version of CorelDRAW. Most people operate on auto-pilot and don't think to save a CDR file down a few versions older if they intend to share the file with anyone. Not everyone uses the latest version. They just his the "save" button, which saves the CDR file in what ever version of CorelDRAW they're using. To make matters worse, the newest versions of CorelDRAW can save back only so far. The current version (2021) can save no farther back than Version X5. They'll probably make X6 or X7 the cut-off pretty soon. I think that policy is really stupid.

It's also possible the person who sent you the CDR file sent you an old CorelDRAW CDR file. The past couple or so versions of CorelDRAW can't read CDR files made any earlier than version 6. I can't remember if CorelDRAW 12 could read CDR files made back to version 3 or not. In recent years the folks at Corel started cutting off all file open/import support for old CDR versions. My guess is they'll cut off version 6 CDR files soon, then version 7, 8, 9, etc. I think this policy is even more stupid than the limitations of how far back one can save CDR files. I guess it didn't dawn on the folks at Corel that some of us long time users might have archive CDR files that go back to versions 3, 4 and 5. Corel's rival Adobe doesn't resort to this nonsense. The latest version of Adobe Illustrator can open AI files made in any prior version, going all the way back to the late 1980's. And Illustrator can save back as far as version 3 (circa 1990).

Another possibility is someone exported the CDR file from another application and the CDR export filter is buggy. But very few rival vector drawing applications have any import or export filters that directly support the CDR format. Inkscape is the only one that immediately comes to mind.