Hi - I have the exact same issue and need help. We have some old pdfs circulating that need to be taken down. They have been deleted from the files ‘folder’ in the designer, but still appear in searches.
Webflow does not delete assets from the CDN when you delete them from the asset panel if ever. You probably would need to reach out to support with a list of them. Hopefully they can map them to your project so they could be deleted. It’s a limitation for sure.