Load Assets into Unity without Asset Bundle at Runtime

Hi,

I am creating an application that depends entirely on assets that are not available at the time of building the project into it's executable.

The point of the application is that a user can select several 3D Engineering CAD files from an Engineering database, that are then converted to OBJ using a separate Java application. This Java application will then pass the details of where these converted files are on the server's file system to Unity, to be loaded into the Unity scene.

I have been looking across all the forums and I see that most answers say that assets need to be built into an asset bundle before they can be loaded into Unity at run time. But i don't have access to the OBJ files i'm trying to show until the application is already running (the user selects the files to be shown while the Unity app is running).

Is there a way I can load these files in on their own? Or, if i do have to create an asset bundle for the newly converted OBJ files, is there a way for me to package an asset bundle without using Unity? In production, I don't want to need to have a Unity license for every machine where the application runs.

I know this is a Unity forum, but if this is not possible with Unity, does anybody know if it is possible using Unreal Engine?