What I would do is create a separate ImageLink app in Admin since you will need to define your base filepath for the .pdfs (you wouldn't be able to use the same imagelink because a base URL is defined for the existing).
If you want to use the same interface, you could. However, I would create another FileResult call on top of your existing mapping. Then use a static value coming in the the messages to base blocking off of so that the correct FileResult call is executed. Does that make sense?
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