How to add my custom document/object user data to File3dm?

I have both document user data and object user data in my plugin.

To keep from data breach, I will not save a 3dm file on local machine.
I keep those data in my document(RhinoDoc) by assign them into File3dm class and change it into bytes.
Then, directly upload those bytes to server.

But I don’t know how to add my custom document/object user data to File3dm.
Is there any way to solve this issue?

Thank you very much.

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