We don’t recommend using emojis in your formatting because there is no way to guarantee how these symbols will appear across devices and apps. Most devices and platforms can’t display emojis - Kindle and Nook will not display emojis, and Kobo will only display emojis on mobile apps, but not devices. Apple Books and Google Play will typically display emojis.
Emojis also will not embed into your PDF file since they are not supported by most fonts.
As an alternative, you might instead try incorporating emoticons. Since emoticons are a sequence of keyboard symbols that represent facial expressions, such as :-) for a smiley face, you’re much less likely to experience compatibility issues.