Boundary command in CAD is the command to create a Pline object (or Region) with shape of a closed boundary line. The origin objects are not disappeared. Below is the way to do:

• Command line: Boundary
• Menu: Draw / Boundary
• Shortcut comand: BO

The below dialog box appears:

Choose and press a point inside the closes area (above picture). When completing this command, a Pline object is created, using MOVE command and move that Pline beside, you get the below figure.

Good luck!

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