How do I get fonts to embed on the form text box portion of a PDF?

I have gone to properties > fonts > embed fonts. All fonts appear on the PDF EXCEPT in the text box form part of the PDF which is a major component of what I’m trying to make.

Hi, I experienced the same issue in Libre Office Writer version: 6.1.5.2 from Debian stable (buster) and version 6.4.5 from buster-backports. Even if the same font is embedded in the document, it is not embedded in the text box. This causes the form to be unusable in Adobe Reader, although it will work using a default font in evince.

Same issue there, running Libreoffice 6.4 (both on Debian & Windows).
The embedding mechanism on PDF files seems broken…
Any hint ?