Welcome to the community, @Seung_Kim! :grinning_face_with_big_eyes: I had to do some digging on .DXF files, and from what I can see, one form of .DXF is just a text file with a .DXF extension. It’s possible that your files are fine, and would only need to be renamed to change the extension back to .DXF after downloading. Then again, there’s a lot that you left out regarding your workflow, so perhaps this wouldn’t be a viable solution.
Unfortunately the vast majority of people here are fellow users, so we can’t officially speak on behalf of Airtable. You might want to write to Airtable support (if you haven’t already done so) to ask about this issue.