Form fields are the legacy way to insert an editable controls in a document (text boxes, checkboxes, dropdowns) by using the FORMTEXT, FORMCHECKBOX and FORMDROPDOWN fields. This includes the legacy Frames (described in OOXML with 'framePr' element). Do not confuse with content controls (structured document tags) (see http://feedback.telerik.com/Project/143/Feedback/Details/113730 ) and with ActiveX controls.