It's impossible to wear out an SSD with the amount of writes MS Office would do.
Absolutely, do install it to an SSD.
*Your saved documents are where you STORE them anyway. Often in the "Documents" folder but you can choose. So to be clear, if you have both an HDD and SSD the optimal setup usually is THIS:
SSD-> Windows, applications, office and similar files
HDD-> backup image of SSD, videos, games (some games on SSD can make sense too like Skyrim with frequent load points)
**I would suggest ensuring you have a suitable BACKUP plan. What happens if any one of your drives suddenly fail. Do you have a plan for that?
I use Acronis True Image to have automated backups weekly (incremental, with auto deletion of older backups). I even have some folders copied from SSD to HDD on a daily basis using Syncbackse Free.