Re: What's this Silverlight thing?
On a related note, I've recently had to deal with people sending me proofs of payment... as XPS files. Which would be fine except none of the Windows 10 apps can read the damn things anymore.
Whoever decided that deprecated apps (Reader) are going to be unable to work at all ("Reader is no longer supported. Go screw yourself."), rather than just no longer updated needs shooting with something very pointy.
I have to send them to our one remaining W7 machine to convert them to PDF.
XPS files are a Microsoft equivalent of PDF files, and are not intended to be editable, so it's not in LibreOffice's primary mission to 'edit the uneditable' - however, all is not lost, there are several third party document viewer applications that will accept xps and oxps files. The Third Party Support section of the Wikipedia article gives a list. The ones for Linux platforms should be able to read the XPS and OXPS documents sent to you.
However, this guide: How to access XPS Viewer in the Windows 10 April 2018 Update might solve your problem without resorting to third party software if you are using Windows 10.