Send and receive documents from/to sharepoint

[SPManiac]

In SharePoint Online, I need to send a document (from doc lib) to a third party software (that is the easy part).

And, after a while that third party software should return modified document back to my SP doc lib (this is tricky part).

What do I need to provide to  that third party for them to be able to return the document back to SP?

[#2]

Hi @SPManiac ,

You could share a document with editing permissions. Once they open, they can edit and changes are going to be saved automatically.

Another way you could do, share a Folder with editing permissions and they can upload from their end.

[#3]

No, I am sending it to software, not a person.
I am sending bytes (of a document) to another software, and that other software needs to return new document to my doc lib (programmatically).