Embedding fonts allows anyone who opens your file to see the document as you intended it to be seen.For a PDF file with fonts already embedded, you may still need to further edit it. To keep font embedded for both of its original texts and newly added/edited texts after editing,please do the following steps:
1:Please first turn on the embed fonts after document editing option in preferences dialog box by going to "File"tab in Foxit PDF Editor>"Preferences”>"Documents",check option "Automatically embed fonts whever text is updated or saved" ,click on "OK" to save the setting.
2:With this option selected, then proceed to use the "Edit>Add Text" or "Edit>Edit Object>Text" or "Edit>Edit Text" tool to edit texts , or "Organzie> Header&Footers" tool to add/modify headers/footers in PDF file,you will find that the characters (a subset of a font) that are used when you edit text objects or headers/footers in the document will be embedded into the document automatically.
Note:The option "Automatically embed fonts whever text is updated or saved" for embedding fonts after document editing is available in Foxit PDF Editor version 12.0 and greater.
How to embed font to a PDF document in Foxit PDF Editor for windows.