What is the issue?
PDF/UA > Basic requirements > Fonts > Font embedding > Font not embedded
What does it mean?
There are one or more characters in a font available and this font is not embedded in the document.
How to fix it?
This issue can not be fixed with axesPDF. You could solve it e.g. with Acrobat Pro. Precondition is that the corresponding fonts are installed on your machine.
Start the tool Preflight in Acrobat. Search for the function Embed fonts (even if text is invisible) and click button Fix.