I open the file before editing, of course. What I meant was, if the file isn't open by the user, like the user's about to edit it. Only when I open the file for editing in VS and then I activate my add-on it works. If I close the file, and activate, then it doesn't (although, I open the file programatically). Nevertheless, I'll take a look at the power toys' source, thanks.
Where it seems there are only borderlines, Where others turn and sigh, You shall rise!