Can Microsoft 365 and third-party application integrate?

[Tianfan007]

Our team have a plan to develop a web application.Here has a requirement: Our application send a DOCX file or XLSX file to Microsoft 365 through any API ,then it will be opened by Microsoft365 online.User who has the passport will view or edit the file online. If user has the "save file" action, the file will be send to our local applicaton as  callback.

I has visited the microsoft graph api,but none of useful be found.

[#2]

Can I suggest that perhaps a Developers form is a better place to ask these kinds of questions. This is more an IT Pro/Admin forum. That said, what you ask should be possible but it seems like a lot of work to me, have you possibly explored the options the power Platform provides? That provides simple, integrated low-code options.