To keep it simple, you can link your buttons to filehosting/filesharing platforms (Nextcloud, Drive, ...) where you host your files and share them for download.

BR

Ricardo

You need to write a controller to return the download response. You can refer to this function in Odoo for downloading PDF reports.

@http.route(['/report/download'], type='http', auth="user")
def report_download(self, data, token, context=None):

In your case, you have to browse the file and return the download response.