Convert to PDF/A gives Warning: PDF version - PDF Document has incorrect pdf version

[PeterGR]

I am trying to embed font into PDF so I can open on other computers with custom font

Using latest Nitro Pro v12.

When I click CONVERT - PDF/A the resultant documents convert then the reports say:
"Warning: PDF version - PDF document has incorrect pdf version"

Why is this the case. Generating and opening in Nitro Pro. Should be smart enough to make it right.
Generated PDF has Document Properties reporting: PDF version 1.3
I have tried converting to
PDF/A-1b and it says should output as v1.4 but generates as v1.3
PDF/A-2b and it says should output as v1.7 but generates as v1.3
PDF/A-2u and it says should output as v1.7 but generates as v1.3