I am not sure whether it has been mentioned or not, but I have long used a handy Word macro written a decade ago by Ferenc Ruzsa. It still works beautifully in my Word for Mac (just as it did when I used a PC). I simply insert it into the macros, and
then assign a keystroke to invoke it (e.g., Command-0). There is one to convert Unicode transliteration to Unicode Devanagari, and another to reverse the process. Just select the text to be converted and press a button. If you want a space between a final
consonant-with-virāma and the daṇḍa, or to force a virāma, you need to insert two spaces after the Roman consonant. The Rom>Dev macro produces nice results in most Devanagari fonts. The macros are attached.