Yes and no. Firstly, emojis will generally not be printed on PDFs. On PDFs the characters in the font Roboto – see https://fonts.google.com/specimen/Roboto#glyphs, in addition to some some basic UNICODE characters, like ™, © and ❶. You have to do a test print to see what works for you.
However, a form designer can paste emoji characters into an element label or a page icon in a form. These emojis should be tested in the apps on the relevant mobile devices as they may not be displayed on all types of systems. Lastly, a user filling in a form can use emojis in the text input and these will generally show on-screen but not on the PDF.
This is a handy site for finding emojis and UNICODE characters and copying them to a form design: http://xahlee.info/comp/unicode_index.html.