Steal the Attributes of an Open Document
Menu: Window Choose the document from the list
Here is another one of those deeply buried, not obvious, and undocumented shortcuts that makes you say, "Doh! I wish I'd known that years ago!" When you are compositing images, it is often useful to make the canvas sizes of all the documents you are using the same. Three different places you can take advantage of this trick are the New dialog box, the Image Size dialog box, and the Canvas Size dialog box. When in any of these three places, you might have never noticed that most of the menus are grayed out and unavailable. However, the Window menu is available. If you choose any open document listed in the Window menu, Photoshop automatically changes the attributes of the New, Image Size, and Canvas Size dialog boxes to match the open document.