You are correct- Either you can attach it via convertkit (which is actually just a download link) or host it on something like Google Drive or Dropbox, then share a public link to it. There are no actual attachments tacked on the email because they are often seen as suspicious. It helps with deliverability to make it a link instead. When you share that link, you can add things like tags and triggers in an automation to help you keep track of the data (if you want to!)
When you're attaching the file and the file name looks "ugly" like "downloadable-file.pdf" you can always change that link by clicking and editing it.