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...
M-Junaid There are different variants of the PDF-standard and PDF/A is one of them that is for long term archiving (https://en.wikipedia.org/wiki/PDF/A). In this standard many requirements must be met, e.g. embedding fonts and do not use certain features. The Office apps (on the client) and therefore the COM APIs support creating a pdf file conforming to this standard, and this issue is about supporting this in the js API as well.