Accordingly, when I checked the cause through the xml file in the docx file, if the hwp file font name includes '&' It was confirmed that parsing error came out due to the '&' character.
When I replaced the '&' character to '&' and save file, I confirmed that the file was opened without any problems. (change all of the '&' (document.xml / footer1.xml / header1.xml / footnotes.xml / endnotes.xml )
This converter is provided by MS. I want to know if MS can fix the error.