For all AutoCAD 2013 and/or 2014 users...
The Longbow Previewer Allows you to quickly preview, process and print AutoCAD file types such as .DWG, .DXF, .DWF, .LSP, .CUIX, .MNU, etc. from within your Outlook and Windows Explorer Preview panes without the need to open the file with AutoCAD!
The Longbow Previewer has no internal Command Line AutoCAD specific functionality, but instead provides extended AutoCAD related user interface functionality to your Microsoft Outlook 2007 or newer and/or Windows Explorer running in Windows Vista, Windows 7 or Windows 8 both 32bit and 64bit.
The image below shows a sample view of the Longbow Previewer previewing a DWG file from within an Outlook email, the exact same functionality is available via your your Windows Explorer. As you can see, the original DWG thumbnail is displayed in the bottom right along with a much improved High-Res version just above it...
.resources - .NET Software Resources previewer
As you can see, right clicking the DWG or DXF gives you access to