Do we have a clean way to add a pdf as an input while creating a session? I am interested in doing that without restarting the server, but I am not sure if it is possible with oTree default functions.

Additionally, is it possible to shape the Configure Session inputs as checkboxes, radiobuttons or selects?

You can't upload a PDF but you can provide a URL of a PDF, which you can then handle appropriately in your python code.

The configure session inputs are checkboxes if it's a boolean value.

If you want to customize it further, you should create your own UI on a separate server and use the REST API to create the session with the desired parameters.