C#

[DllImport("USER32.DLL")]
public static extern HHOOK SetWindowsHookEx(int idHook, HOOKPROC lpfn, HINSTANCE hMod, DWORD dwThreadId)

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"All programmers are playwrights and all computers are lousy actors."

void Timer(object sender, System.Timers.ElapsedEventArgs e)
{
    if( InvokeRequired )
    {
        Invoke(
            new System.Timers.ElapsedEventHandler(this.Timer), 
            new object [] { sender, e }
        );

        return ;
    }
 
    ...
}

FileAttributes fa = File.GetAttributes(@"C:\TheFile.txt");
                                                                                         
if((fa & FileAttributes.ReadOnly) == FileAttributes.ReadOnly) // Write protected?
{
     // Yes it is!
}