Open two instances of a file in a single Visual Studio session

I have a file, xyz.cpp. I want to open two instances of this file in Visual studio (BTW, I am using Visual Studio 2005). Why would I want to do so? I want to compare two sections of the same file side by side. I know workarounds such as:

1. Make a copy of the file. But the problem is that it's not elegant, and I don't want to make copies every time I am faced with this.

2. I can split the window into two. The problem with split it that I can split it horizontally only. The result of a horizontal split is that the right half of my screen is white space.

If I were able to split it vertically or open two instances of the same file, it would increase the number of lines of code I can compare.

Here's how to do it...

1. Select the tab you want two copies of
2. Select menu Window → New Window from the menu.
3. Right click the new tab and select New Vertical Tab Group

If New Window is not listed in the *Window menu note that the command does exist, even as of Visual Studio 2017. Add it to the Window menu using menu Tools → Customize → Commands. At that point decide where to put the New Window command and select Add Command.

UPDATED on "30 July 2018"

In Visual Studio Code version 1.25.1 and later

Way 1

You can simple left click on your file in the side-panel (explorer) and press Ctrl + Enter.

Way 2

Simply right click on your file in the Visual Studio Code side-panel (explorer) and select the first option open to the side.

For Visual Basic, HTML and JScript and RDL Expression, the Window > New Window option mentioned in PaulB's answer is disabled. However an option can be changed in the Registry to enable the menu item.

All other languages do not restrict to a single code window so you can use PaulB's answer without editing the registry.

Enabling New Window in Windows Registry.^{[1] [2]}

1. Go to the following registry key. This example is for Basic (Visual Basic), but the key is also there for HTML, JScript and RDL Expression.

   • 64-bit OS: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\10.0\Languages\Language Services\Basic
   • 32-bit OS: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\10.0\Languages\Language Services\Basic

2. Find the value Single Code Window Only and do one of the following:

   • Set it to 0
   • Rename the value
   • Delete the value (use caution!)

This will enable the "New Window" menu item, but it may still not be visible in the menu.

Adding Menu Item

To actually see the New Window menu item I had to add it back into the menu:

• Tools > Customize... > Commands > Add Command...
• Select 'Menu Bar' the select the 'Window' menu in the dropdown
• Add Command... > Window > New Window > OK

Restoring Registry Value
Copy-paste this to notepad, save as a .reg file and import the file into your registry to restore the initial setting.

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\10.0\Languages\Language Services\Basic]
"Single Code Window Only"=dword:00000001

Go to menu → Windows → New Window:

You can use the Windows → New Window option to duplicate the current window. See more at: Why I like Visual Studio 2010? Undock Windows