this is not a question but kind of a request.
I have tried to find right place to post
(asked to msdn forum, partnership support, ...)
but failed.
why microsoft gives me this difficulty?
can't place a total official support page?
anyway, this is not the subject of this post.
someone suggested me to post here.
(https : // social.msdn.microsoft.com/Forums/en-US/11fd7f37-bec6-4201-b5ce-085f24446362/forum-for-office-365-filehandler-addin?forum=whatforum)
I asked this question before, and I know it is impossible at current time.
(http : // stackoverflow.com/questions/36172056/can-i-make-office-365-file-handler-for-existing-file-format-docx-xlsx-pptx)
but I need that feature. (open docx file with custom file handler)
so I want to request microsoft to support this feature.
and want to have clear answer thought it will be "never available."
if replacing associated webapp(office online) is unacceptable,
way to add new context menu item is enough, I think.
(like google drive does - https : // developers.google.com/drive/v3/web/integrate-open)
possible with custom action of file handler 2.0