You can add fonts to the Font Family list in the editor toolbar - https://www.joomlacontenteditor.net/support/tutorials/editor/adding-and-removing-fonts I am unfamiliar with the process of adding fonts to SP PageBuilder amd assume they are loaded by SP PageBuilder dynamically. For the fonts to be rendered correctly in the editor, you will need to create a stylesheet that includes @import rules for the fonts, eg:

/* Donegal One Font */
@font-face {
    font-family: 'Donegal One';
    src: url('fonts/DonegalOne-Regular.eot'); /* IE9 Compat Modes */
    src: url('fonts/DonegalOne-Regular.eot?#iefix') format('embedded-opentype'), /* IE6-IE8 */
         url('fonts/DonegalOne-Regular.woff2') format('woff2'), /* Super Modern Browsers */
         url('fonts/DonegalOne-Regular.woff') format('woff'), /* Pretty Modern Browsers */
         url('fonts/DonegalOne-Regular.ttf') format('truetype'), /* Safari, Android, iOS */
         url('fonts/DonegalOne-Regular.svg#DonegalOne-Regular') format('svg'); /* Legacy iOS */
    font-style: normal;
    font-weight: 400;
}

Assuming the font files are in a "fonts" folder in the same folder as the stylesheet. Then and add this as an additional stylesheet for the editor to load: 1. In Editor Profiles -> Editor Parameters -> Typography, set Editor Styles to Add. 2. In the Custom CSS Files field, add the relative path to the new stylesheet.