well you really cant add emojis that others will see. You may be able to see them, but unless someone else has this modified font, it wont send over. especially to phones and tablets
Emojis look different depending on what platform the end user has. There is a whole webpage dedicated to it at https://emojipedia.org/ . Its basically a font that has to be read by the end users device and not just a simple just add them in. There are organizations that make a set of standards when it comes to emojis so that can be used across platforms. When you send an emoji, its not the picture you are sending, but a line of code that tells the end user device what image to show.