What I did: Attempted sharing and attaching a PDF document to a new Agenda note. I attempted this from several different source apps.
What happened: I was unable to find Agenda listed in the available apps for sharing the PDF file. I was, however, able to manually copy and paste the document into a new Agenda note.
What I expected: I expected to find Agenda in the available apps for sharing, as in iOS 12.
Things that might be helpful to know (Agenda version, OS and model, etc): This condition is present for me on latest Agenda version in iPadOS 13.1.1, iOS 13.1.1, and macOS 10.14.6. Hardware in use: MacBook Air (Retina, 13-inch, 2018), iPad Pro (12.9-inch) (3rd Generation), iPhone SE