Thanks for you help, I'm grateful.
I checked your test app and it's working but I struggle with one thing, which is to find the exact URL of the file I need to import.
In fact, my user can, with just a click, "share" a file or all the files in a zip file with any share solution installed on his phone. This works great.
But the reverse is much more complicated.
Is there a possibility for the user to receive a file as an attached file to a mail, and to put this file in the ASD through the app ? If not, how can I put the file on the internet with a direct URL that downloadtoASD will be able to cope with ? most cloud services give links to webpage with buttons to click to download the file :-/