C# Generate Random Number on Program First Startup and Keep it the Same Every Time it is Ran Again For a File Password

I am making a log system for my app, but don't want the user to edit the log. I want the app to get a random number for this password, but I don't want it to be the same for other users of the program, to keep each log as safe as possible. But I don't know how to do this, while being able to have the password be the same every time the app is started. How should I go about this? Thanks in advanced!