Get ( SystemIPAddress ) might be helpful. If the iPads connect to the local network in the office the IPs will be in a defined range and you can go directly to the hosted file; if they're on a remote network the IP address will be outside this range and you can open the local file.
So I need an intermediate file to run this script, but it seems to make sense. I fear that the mobile wifi boxes we use outside the office assign IPs in the same range, but I guess those can all be configured or I can reconfigure the office IPs.
With a calculation I can easily discriminate the network. Thank you for the idea.