Move open Excel document to separate window

Interesting idea. I'm reasonably confident that you cannot do this without a custom macro. Being a rainy Sunday...

Sub OpenInNewInstance()
     Dim objXLNewApp As Excel.Application
     Dim doc As String

     doc = ActiveWorkbook.FullName
     ActiveWorkbook.Close True

     Set objXLNewApp = CreateObject("Excel.Application")

     objXLNewApp.Workbooks.Open doc
     objXLNewApp.Visible = True
End Sub

Assuming you're not familiar with VBA, you'd need to:

1. Copy the code above
2. With a new Excel workbook opened, open Excel's VBA editor (Alt+F11)
3. Right-click on VBAProject (Book1) (or whatever it's called in the left menu)
4. Select Insert > Module
5. Paste in the code into the main window
6. Back in Excel, select another workbook to test the code on (it'll save the workbook before it closes it)
7. Go back to VBA editor, select the module you pasted in and press the play button

I have 3 versions of Excel installed on my machine, and when I run this in Excel 2010, it opens a new instance of Excel 2003.

If this suits your needs, you could package this into an add-in and have it available as a ribbon button. Let me know and I can help out if you're unfamiliar with doing so.

Edit: If this approach works for you, obviously there would be some additional code to add in that would ensure the new instance of Excel is maximized in another window. Let me know.

I don't have a way to "tear off" a sheet into a new window, but if you know from the start that you'll want two windows, this is the quickest way:

Open your first file as normal. SHIFT + CLICK the Excel task bar button (at the bottom of your screen, between the Start button and the clock). This will force Excel to open a new instance as a separate window. Go into that new window and click File -> Open to open the second file. Rinse and Repeat as needed for multiple windows.

Unfortunately, if you like to double-click on files to open Excel, you'll have to break that habit for the second window, which is my usual problem. But with some forward thinking, there's no easier way.