Use Colophon from the share sheet

From the iOS Files app

Long-press a PDF in Files and choose "Add to Colophon" from the share sheet to add it to your library. Switch to Colophon and it'll ask what you'd like to do with it.

From Finder on Mac

The same extension appears under Finder's Quick Actions (right-click a PDF, or use the Preview pane), so a PDF sitting anywhere on your Mac can go straight into Colophon's library. The first time, macOS requires a one-time step to turn it on: open System Settings → General → Login Items & Extensions → Extensions and enable "Add to Colophon".

What you can do

Once the PDF is in your library, Colophon presents three choices: Read opens it for viewing, Edit jumps straight into edit mode, and Ask for Insights opens a chat about the document immediately — though that option only appears when Apple Intelligence is available on the device.