How to make AutoCAD open a new instance of AutoCAD not a new Tab or vise versa

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Double-clicking a DWG file opens a new instance of AutoCAD

Issue:

When double-clicking a DWG file in Windows Explorer (or when opening it from within AutoCAD), each drawing launches in a separate instance of AutoCAD.

Causes:

  • The SDI (Single Document Interface) system variable is set to 1. This regulates whether or not multiple drawings can be opened in a single interface.
  • DWG files are not associated in Windows with the "AutoCAD DWG Launcher" application but are instead associated with an AutoCAD acad.exe file.

Solution:

Do the following, testing double-clicking a DWG file after each procedure:
  1. Check the SDI system variable.
    1. Exit all instances of AutoCAD.
    2. Launch the program again (do not double-click a DWG file) and start a new drawing.
    3. On the command line, type SDI and press Enter.
    4. Confirm that it is set to 0.
  2. Re-associate DWG files with the AutoCAD DWG Launcher (see DWG file type associativity in Windows).
  3. Elevate or de-elevate permissions of AutoCAD and the AutoCAD DWG Launcher (one way or the other may correct functionality):
    1. Locate the following two files:
      C:\Program Files\Autodesk\AutoCAD 20xx\acad.exe
      C:\Program Files\Common Files\Autodesk Shared\AcShellEx\AcLauncher.exe
    2. Right-click each file and choose Properties and then the Compatibility tab.
    3. Toggle the setting "Run this program as an administrator." and then click OK.
  4. Install (or uninstall and reinstall) the same version of DWG TrueView that matches your copy of AutoCAD (see Where to download previous versions of DWG TrueView).
  5. Apply the registry edit solution found in Error: "Windows cannot find..." .dwg or acad.exe or acadlt.exe when double-clicking a DWG file to open in AutoCAD (see warning below).
    • As an example, for AutoCAD Mechanical 2018:
      1. Exit AutoCAD Mechanical 2018.
      2. Press WINDOWS-R on the keyboard to bring up the Run window, enter REGEDIT and click OK.
      3. Navigate to and select:
        HKEY_CURRENT_USER\Software\Autodesk\DwgCommon\shellex\apps\{56A0F03C-50A5-425e-B919-1E5E40FA0168}:ACADMPP.
      4. Edit the keys OpenDdeSvc and PrintDdeSvc to both have the value of AutoCAD.r22.DDE.
User-added image
  1. Reset AutoCAD to defaults (see How to reset AutoCAD to defaults).
  2. Apply the following registry edit solution (see warning below).
    1. Delete the following registry keys:
      HKEY_CLASSES_ROOT\.dwg
      HKEY_CURRENT_USER\Software\Classes\.dwg
      HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.dwg
      HKEY_CURRENT_USER\Software\Microsoft\Windows\Roaming\OpenWith\FileExts\.dwg
    2. Associate a DWG file with AcLauncher.exe or acadlt.exe.
  3. Uninstall and reinstall AutoCAD (see Performing a Clean Uninstall).

Warning! 
Problems caused by improperly editing the Windows registry could render your computer operating system unusable. Microsoft provides a wealth of critical information that you need to know about the registry in the Microsoft KnowledgebaseUse the Microsoft Registry Editor only at your own risk and only after backing up the registry as outlined for your operating system in the Microsoft article How to back up and restore the registry in Windows and in the related solution How to back up the system registry. Additional information about the registry is also contained in the Help topics in the Microsoft Registry Editor.

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