To highlight text in bold, place asterisks on both sides of the input box: *Text*.
In WhatsApp such text will be displayed as follows:
To highlight text in italic use underscores: _Text_.
To apply strikethrough to text, use the tilde symbol: ~Text~.
To highlight text in monospaced font use three apostrophes: ```Text```.
Note that if you want to send text that contains underscores, you must shield the text with a backslash before highlighted word, for example: text\_with_underscores
Then the client will receive the correct text. Otherwise the word in the middle will be italicized and the underscores will be missing.