Hey @liaofranklin11! We have a guide on setting up paid newsletters here14 (even if your product isn't a paid newsletter per se, most of that info also applies to other recurring products as well, such as how to only filter those emails to go out to currently paying customers).
As for sending the file(s) via ConvertKit, linking it to the email as a PDF (guide here14 under 'Files') is probably the most straightforward option but you can also upload it to your own website or Dropbox/Google Drive/etc. and link to there from the email, as well ☺️
Let us know if you have any more questions!