Something similar was just recently asked so I will link to it:
What you will probably want to do is have your file sent to the server to be stored somewhere (like a data table) and then use an HTTP endpoint to retrieve the file and serve it your your other application using a link to the endpoint:
Also,
If this is running on another machine, you should probably look into using anvil-uplink instead, but if “your code” is running the client browser and anvil is just embedded in the page then I don’t think you will be able to get a “link” any other way.