Attaching external files is not necessary in your newsletters. But there are two ways you can still share file information:

1. Create landing pages and link them in buttons, text and images in your mailings.
2. If you do not have the opportunity to add your files/documents to your own website/landing page, you can place your PDFs or other documents on, for example, Google Drive or Dropbox and create URL links there - which you then use to link to text or image in your mailing.