Save to vpn-connected cloud

I'm running MS 365 on my Samsung Ultra 24 android phone. When using MS Word and choosing the "save as" option, i am given a number of options such as this device, one drive, drop box etc. However I want to save to my NAS via the VPN that connects both my phone and NAS. Can this be done? Is there an Android app that integrates with MS 365 for this purpose?

TIA ... Greg