Most computers today come with a trial version of the program install that only works for 30 days. MS uses this to get you hooked on the program, and then has it expire so that you will have to pay to buy it. It is not a free part of Windows.
Go out and download either OpenOffice or LibraOffice. They are "clones" of the Word (excel, Powerpoint, etc.) programs that are 100% free. They have been around for years and are safe to use.
The files created, and saved in "doc" or "docx" format are 100% identical to files created in Word. Either can open, read, edit and save existing Word files.