AcroForm

AcroForm is the name of the PDF standard’s form model. A form field has a name, a type and a value, and one or more widgets: the boxes on the page where it is drawn and filled in.

Because the values are stored by field name, an app can read and fill a form from code as well as on screen — the basis of most PDF form automation.

The standard has four kinds of field: text, button (push buttons, checkboxes and radio buttons), choice (list boxes and dropdowns) and signature. Each one is stored in the document’s form data, and a separate appearance tells a viewer how to draw it, which is why a filled form looks the same in different viewers.

AcroForm isn’t the only form format you will meet. XFA is an older XML-based format that some government and enterprise forms still use, but it was deprecated in PDF 2.0, and many viewers don’t support it. AcroForm is the one to design new forms in.

Field names matter more than they look. A clear, unique name such as patient_last_name lets an app fill the form from a database and read the answers back without guessing, so name the fields before the form goes out. When a form is final it can be flattened so the values can’t be changed.