How to implement partial file synchronization?

Question

Android

Sorry, maybe the title turned out to be clumsy - I don’t know how this action is called correctly.
The bottom line is ... I work with pdf books from different devices (android & windows), while I actively edit these books (comments, highlights, links, footnotes, etc.).
Naturally, I want all my changes to be synchronized when opening a file from any device. But the problem is that my mobile Internet is not unlimited, and I cannot afford to drive back and forth a file weighing tens - hundreds of megabytes many times.
The solution would be partial synchronization, when only the changed parts of the file are downloaded. I know that such functionality is implemented in dropbox, but, unfortunately, it does not work on the mobile version of the application. I would be grateful if someone could tell me how to implement such a mechanism. Thank you.

Answer 1

it is easier to connect an unlimited tariff, now it is not very expensive.

Answer 2

I know that such functionality is implemented in dropbox, but, unfortunately, it does not work on the mobile version of the application.

Specify pliz in which version of which application it does not work?
under android, the dropbox client is perfectly set and works.
Both the traditional rsync and the now fashionable bittorrentsync can drive over the network only the difference between files.
If your storage needs fall within the free dropbox limit, I suggest looking into it anyway.