I do not know if you can do it in an async way (should be definitely possible), but a basic approach would be to create a simple javascript function to toggle a refresh when a selection is made and you could change the link to be accessed. I have used a similar approach (dropdown + iframe for images) with images and a flask server in python, so it should be possible with pdfs too in iframe.
How to Embed PDF Document in HTML Web Page - CodexWorld
Use of UiPath robot in your workflow here, I am not so certain. May be a little overkill.
Hope this helps!