I am working with onlyoffice document server and it provides conversion from html to docx but is that possible to convert vice versa i.e. (docx to html)?
Any help will be appreciated. Thanks.
That is impossible in this version. Conversion to HTML will be released soon. The only way to get HTML output in the current version is "File>>Download as" in the Document Editor's interface where HTML is listed as one of the supported output formats.