If you are a Pro or Enterprise level customer, custom fonts can be imported into your account. This is currently handled only by the Singular Support team so please submit a request and attach your font files.
Custom fonts, when used in Singular, have the potential to run into rendering issues. Make sure to provide Singular with web-designed/optimized fonts in WOFF format. Singular also supports the 700+ free Google font library where you can find web-optimized fonts.
For more information on using custom fonts in Singular, visit this article.