Click and dragging objects in Vectorworks simply moves them around the page. To duplicate an object, you can use Edit > Duplicate, then move the new copy to the desired location. To shave a few seconds off this process each time you wish to do it, simply pressing and holding the Alt (Windows) or Option (Mac) key on the keyboard, will make a small "+" appear next to the cursor.
This indicates that if an object is clicked and dragged, instead of moving the original, a new duplicate object will be created and placed at the new location upon letting go of the mouse button.
Edited by JimW