How do I persist file-independent variables in VSTO that can persist even after the Microsoft Office has closed

I am using VSTO (visual tools for office.) I need to store a variable that is file-independent (so I cannot stored it in a file meta-data as 开发者_运维问答in this question) and can persist after Microsoft office has closed and been restarted. How can I do this?

Note Is there any way built into VSTO? I want registry, XML, or SQL server ce to be the last resort

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There are a plenty of ways to do so:

1. Store your data as XML serialization in specific file under predefined direcotry (e.g. %appdata% folder).
2. Store your data using web service which provides data storage (your own web service or remote database, etc.).
3. Store data in system registry as values located in predefined registry key.