How do I make LibreOffice Writer embed a custom font when exporting to PDF?

I’ve created a PDF form that uses a few custom made otf fonts. I can embed them in the odt file through file properties which balloons size from 845kb to 13mb+ but the PDF that I export (using these options) is only 46Kb, so it doesn’t have the fonts embedded. I’m filling this form out programmatically (using PDFBox) so I’d like the fonts embedded for when my application is run on systems that don’t have the fonts installed. I’m using LibreOffice

Link to odt.

Link to PDF.

Try exporting to Archive PDF/A-1a (ISO 19005-1) by ticking the corresponding box further up in the dialog. The PDF/A-1a format is intended for long-term preservation, and all fonts that used in the source document will be embedded into the generated PDF file.