If your document contains mathematical symbols, scientific symbols, non-Latin alphabet characters, or other unusual characters or fonts, you will need to embed these fonts in your document so that readers whose computers do not have these fonts installed can view them. Failing to embed fonts can result in readers seeing the wrong characters (or no symbols at all) in your document.
In Microsoft Word, you can embed fonts by going to File > Options > Save tab. Under "Preserve fidelity when sharing this document", check "Embed fonts in the file" and "Embed only the characters used in the document (best for reducing file size)".
The next time you save your document, the fonts will be embedded in the document. Note that this may greatly increase the file size of your document.
Also note that Word may be unable to embed some fonts, such as those that are copyright-protected by their authors.