public static PDField createField(PDAcroForm acroForm,
    COSDictionary field) throws IOException 
{
        PDField pdField = new PDUnknownField( acroForm, field );
        if( isButton(pdField) )
        {
            int flags = pdField.getFieldFlags();
            //BJL, I have found that the radio flag bit is not always set
            //and that sometimes there is just a kids dictionary.
            //so, if there is a kids dictionary then it must be a radio button
            //group.
            COSArray kids = (COSArray)field.getDictionaryObject( COSName.getPDFName( "Kids" ) );
            if( kids != null || isRadio(flags) )
            {
                pdField = new PDRadioCollection( acroForm, field );
            }
            else if( isPushButton( flags ) )
            {
                pdField = new PDPushButton( acroForm, field );
            }
            else
            {
                pdField = new PDCheckbox( acroForm, field );
            }
        }
        else if (isChoiceField(pdField))
        {
            pdField = new PDChoiceField( acroForm, field );
        }
        else if (isTextbox(pdField))
        {
            pdField = new PDTextbox( acroForm, field );
        }
        else if( isSignature( pdField ) )
        {
            pdField = new PDSignature( acroForm, field );
        }
        else
        {
            //do nothing and return an unknown field type.
        }
        return pdField;
}

This method creates a COSField subclass from the given field. The field is a PDF Dictionary object that must represent a field element. - othewise null is returned