Under More, to the left of the template preview, use the Copy fields/document button to be forwarded to the Document Functions page, as in the section above.
To duplicate individual fields onto the same page:
Hover the cursor over a field
Press ' d ' on the keyboard
A copy will appear below the original field, with the same validation type, and a +1 to its Field Order
To duplicate individual fields onto other pages :
Click on a field to reveal the field properties menu
Click on Duplicate, near the bottom of the menu (just above Save, see left)
A copy of the field will appear on the selected page(s), with the same validation type
To duplicate whole document fields, see here.