Where was the file stored? Locally? Or iCloud? OneDrive?
If local and if you do have a backup of your iPad from before the file was lost/deleted/gone’d, it might be possible to restore that. This only if the lost/deleted/gone’d file was local to the iPad. This will not work for a file hosted on iCloud or OneDrive. That will mean reverting all of your iPad contents and all of your data to that backup, which can be painful, and gets more painful the further back the most recent backup. (Back up the iPad again anew elsewhere, restore the old backup, get the file, and reset and restore the current backup, to try to avoid reverting everything.)
If the file was stored in iCloud, log into iCloud and see if you can restore the file there.
As for OneDrive recovery of files, donno, ask Microsoft, etc.
If the file is not stored in Files locally, or stored in iCloud Files, or in OneDrive, or in Microsoft 365 somewhere, and if there are no backups, and particularly if the app vendor sent you here, then the file is likely gone. There’s nothing to recover.
We all learn about the need for backups, and about tools sometimes losing things, and about our own errors, and unfortunately it may well be your turn.