Downloadable Files lets you host files like PDFs, show notes, and bonus resources for your listeners — you'll find it under Settings → Downloadable Files, available on the Pro plan and above. You can upload a maximum of 10 files in total.
The limit exists to prevent abuse of the feature. It's set at a level that comfortably covers how podcasters typically use it, while keeping Podpage from becoming a general file-hosting service. It counts total uploaded files, so you can always delete older files to make room for new ones.
Need more space? File-sharing services like Dropbox and Google Drive offer generous free plans — upload your files there and paste the shareable links into your show notes, blog posts, or pages. See Can I upload a PDF to my website? for a walkthrough.