Make sure it isn't localized to mm instead of inches within:
Machine Status > Machine Setup > Localization
As for Windows 10, Xerox never developed a driver, but the one from Win 8 works
So if it is happening in every program, not just Word. go to Control Panel > Devices and Printers
Right click the printer and go to Printer Properties > Preferences > Paper/Quality > Advanced > Fit to page = Nearest Size and Scale
If it is only in Word, it would be found here (Application will always over-ride a driver), Mine shows Letter though in Win 10 x64 MS Office 2016
I looked at the MS Class driver that comes with Windows 10, it has much less of a feature set, so use the Win 8 version from Xerox instead.
Hello, my wife's non-profit organization recieved a donation of a used workcenter m20i, and for the most part it works fine except it keeps trying to print on A4 paper even though I set the tray to Letter, and set the printer preferences to Letter. But when you open a Word document, and try to print, again the paper format is set to A4. The PC is running on Windows 10, and I noticed the Print Device is a m20, no m20i, I removed that driver, I added a new printer, but no change (probably because Windows is using the same driver).