How to add hindi font in ms word?

It's quite simple, actually. You don't add the font to Word directly. You must install it on your Windows system.

First, download a popular Hindi font file, like Kruti Dev (.ttf). Right-click on the downloaded file and choose 'Install'. After it's done, just restart MS Word. The new font will now be available in your font list. For typing, you should also add the Hindi keyboard layout in your main Windows language settings.