you need to install nepali fonts if you want to type in Nepali.
here is the link: http://www.nepali.info/nepali/fonts/ read how to install at the bottom of the page.

 install Nepali unicode from http://www.madanpuraskar.org/downloads.php i have been using the same, It works in win xp vista n win 7 best of luck

you wont be able to open the document in other computer if you write through nepali unicode so it will be better if you write those by insalling nepali font in your computer..

For that I suggest you use Nepali Unicode! There's option to convert Nepali Unicode to Preeti Unicode too! Hope there will be no problem when using Nepali Unicode  

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.