Converted pdf/A document is not validated by adobe preflight tool


I'm trying to convert PDF to PDF/A-2a using PDFTron PDF/A Manager V6.2023831. Please help me to pass Adobe Preflight tool pdfA/A2 compatibility check.

Please find original ( and converted( by PDF/A manager files uploaded

The problem is that Adobe Prefilgth tools shows errors when converted file is checked, like
The unicode for cid 3 is unknown.
The unicode for cid 18 is unknown.
The unicode for cid 19 is unknown.
The unicode for cid 20 is unknown.
and so on.

However converted file is displayed properly and no error is shown by PDF/A Manager when it checks converted file for PDF/A confirmance.

I've checked converted file and found that there are /ToUnicode entry for Arial fonts. So from my point of view it should be enough to map characters to Unicode.

Is it possible to add cmap with pdfa.exe utility to the converted file for certain cids ?
Is it possible to add cmap table for missed cids to the original file using PDFNet SDK?

Should I embed font to the original PDF document before it is being converted to pdf/A-2a format as it described in RemapFontEncoding Google Groups ?

Thank you