Get yourself a portable USB DVD drive. $10 to $20, depending.
Or, go here and download an earlier version of office. Requires your key.
https://www.microsoft.com/en-us/software-download/office Download Earlier Versions of Office
Alternatively, you can use a drive emulator. I have used one called Virtual CloneDrive for a number of years. It is free for home use and available on all sorts of download sites (pick one you trust that has it).
- On your PC, extract the CD/DVD contents as an ISO file. Alternatively, use Al's link to download the ISO file from Microsoft.
- Move this file to the NUC.
- Open (mount) the file using Virtual CloneDrive.
- Install Office from mounted image as if you were doing it from CD/DVD.
Hope this helps,