You can type Nepali in MS Word in two ways: Preeti font or Nepali Unicode.

For Preeti font, first download and install Preeti font here:
https://merokalam.com/preeti-font-download/

Step-by-step guide for typing Nepali in MS Word:
https://merokalam.com/blog/how-to-type-nepali-ms-word-preeti-unicode/

If you want to type Nepali without installing anything, use this online Nepali typing tool. You can type Roman English like “namaste” and get नेपाली Unicode:
https://merokalam.com/easy-nepali-typing/

For typing practice, use Typeshala Online:
https://merokalam.com/typeshala/

For Preeti keyboard layout and key positions:
https://merokalam.com/blog/nepali-font-keyboard-layout/

If you already have old Preeti text and want to convert it to Unicode:
https://merokalam.com/preeti-to-unicode-converter/

More Nepali font download options:
https://merokalam.com/blog/nepali-font-download/

Hope this helps.