Configure your RocketBook app to include a destination in iCloud (and specifically the OCR’d text). This is at least a destination Drafts can access, as there is no web API for Drafts and Rocketbook works with explicit destinations the app is coded to work with.
Then, once saved to iCloud, you could either create a Drafts action or an Apple Shortcuts shortcut to move files from the Rocketbook app folder to the Draft Inbox folder in iCloud. Now you may (I haven’t tested if this can run in the background) be able to do this using a Shortcuts automation to trigger a shortcut. But inevitably you would have a delay (as the shortcut would be triggered at a specific time or times), or need to trigger manually.
If you happen to have a Mac running 24x7, you could have that move the files in iCloud automatically for you using a folder watch automation, Hazel rule set, or a Keyboard Maestro folder trigger.
Once the files move, you need to have a device running Drafts (just one) set to import from the inbox folder.
Hope that helps.