Patrick, I don't think the issue is with the printer system, so resetting it won't make any difference, as the OP reported. As for "appropriate software," I do not install any printer drivers from the manufacturers on my Macs. I just use what is included from Apple, finding my printer make and model in the list when I set up the printer. I did try once, because someone said I should, but the drivers really screwed up the whole printer setup, so I deleted all of it, removed the printer, rebooted the Mac and re-configured the printer with the Apple software again.
And I use AirPrint, so the suggestion that pine man got was pretty much bogus, IMHO. The fact that other MS365 products (Excel, for example) print double sided perfectly well points to something awry in the Word installation. I use MS365 and double sided printing is in Word for me, and it is "sticky" for me and doesn't require any special actions to use repeatedly. Of course, if I turn it off, it does have to be turned on again, but if I don't touch, it stays the default. So, it works, generally. He has something wrong in his system.