The https://docs.microsoft.com/en-us/javascript/api/office/office.document?view=word-js-1.3#getFileAsync_fileType__callback_-API already supports PDF export. Unfortunately, the file format is PDF 1.8...
@lindalu-MSFT
This would be a great extension, not being able to create a pdf/a is a showstopper for many public sector applications since they require using pdf/a instead of plain pdf files.