Hi Katherine,
Hit Windows key + R together, enter: optionalfeatures
Just check once more to see if the "Microsoft XPS Document Writer" exists, at least it pops up on my Windows 10 with 1803. Check that if not already, click OK. Now we need to bring back the XPS Viewer.
Go to Start, look for "Apps & features", then click that. In the new window under Apps & features, click Manage optional features. Click "Add a feature", then look for XPS Viewer, and click the Install button that pops up.
If this doesn't work at all, please provide me with your Windows 10 edition (Home, Pro, Enterprise), and I can look into this further for you.
Let me know.