I think you had MS Office starter version on you PC. MS Office starter is a limited function version of MS office suite & has basic office functionalities like Word, Excel & PowerPoint. It comes with a new brand PC or Laptop. PC & laptop brand supplier is responsible for providing support of MS Office Starter. You can use it for forever because it is not trial version of MS Office suite.
How to re-install MS Office Starter: If you have uninstalled the MS Office starter from your control panel then you may still able to re-install it from MS Office program manager.
Alternative: If you don't want to buy MS Office then there are some good alternatives available on the internet like Libre Office, Open Office..
Ref: See this link