Why not just switch to it and quit it without opening a new Window?

That's the whole paradigm. Windows belong to applications, but applications aren't windows. That's one reason the menu bar is divorced from any window (along with Fitt's law): so that you can interact with an app even when it currently has no windows open.

You know you could just close it from the Dock or application switcher, right?

Yes but that requires a click-and-hold, causing the whole dock to resize for the pop-up menu, which is quite slow on my 32-bit MBP maxed out at 2GB RAM. I find it quicker to just click the Preview icon (causing a new window to open as the focus switches), and command+q.

You might want to try command-tabbing and quitting.

Basically with command held down the entire time, hit tab until Preview is framed, and instead of releasing command (which would pull Preview to the foreground), hit Q, which will send Preview the command-q event and cause it to quit.

> Some times I reopen a window of preview let's say just to close the whole program.

I do not understand what you are saying. Can you elaborate?

Here is a scenario, and my mac is a month old, so maybe I am borrowing heavily from Ubuntu and MS experiences. When I am reading two pdfs, and then close one, it makes sense for the preview menu to stay on because I am reading the second pdf, but when I close the second, what reason is there for preview menu to stay up?

Edit: As to my original comment, when I switch to another app, preview stays open, but up to now I don't know how to close it because I can't get the menu to appear without a pdf or something using it, that's why I reopen a document, forcing the menu to show up, then close the app.

There's lots of reasons for the menu to stay open; the simplest example is clicking File, then Open, to open a new file.

As far as the menu disappearing when you close both documents, that's confusing and directly contradicts what you typed earlier. I can open Preview.app, and it'll just show me the menu. I can close it by alt-tabbing to it and hitting Cmd-Q - no windows required.

> Some times I reopen a window of preview let's say just to close the whole program.

You could just close it from the dock you know. Or switch to it and command-Q immediately.

In fact, I don't even understand how you'd go around to "reopening a window" of preview, preview will not open any window without a document in it, do you open a document just to close preview or something?