Where does IFormFieldObject live in the IronPDF API?

IFormFieldObject is in the IronSoftware.Forms namespace, shipped in IronPdf.dll. It is one of three contracts composed into IFormField, alongside IFormFieldAnnotationObject (geometry) and IPdfDocumentObject (document identity). Concrete classes such as TextFormField and SignatureFormField implement IFormField and so inherit the IFormFieldObject data surface a developer reads and writes.

What is the difference between IFormFieldObject, IFormFieldAnnotationObject, and IFormField?

IFormFieldObject defines the data members of a form field: Name, FullName, Value, FormType, MaxLength, ReadOnly, Choices, and related properties. IFormFieldAnnotationObject defines on-page geometry such as X, Y, Width, and Height. IFormField composes both contracts together with IPdfDocumentObject and adds the SetDefaultFont method. Concrete form field classes implement IFormField, not IFormFieldObject directly.

How do you read or write IFormFieldObject properties on a loaded PDF?

Call PdfDocument.FromFile to load the document, then call FindFormField on the Form collection with the field name. The returned IFormField exposes every IFormFieldObject property: read Name or FullName to identify the field, check ReadOnly before assigning Value, and consult Choices to enumerate valid options on combo-box and radio fields.

Interface IFormFieldObject

Q: What implements IFormFieldObject in IronPDF?

Every concrete form field class implements IFormFieldObject by inheritance through IFormField. Those classes are TextFormField, CheckboxFormField, ComboboxFormField, RadioFormField, SignatureFormField, and ImageFormField. They are returned as IFormField from the form field collection, so the IFormFieldObject data members are accessed through that reference.

Form field object

Inherited Members

IPdfDocumentObject.Client

Namespace: IronSoftware.Forms

Assembly: IronPdf.dll

Syntax

public interface IFormFieldObject : IPdfDocumentObject, IPdfDocumentObject, IDocumentObject

Reading a fillable PDF form field's name or writing its value in IronPDF, independent of where the field sits on the page, runs through IFormFieldObject. It declares the property surface that identifies a field and carries its current value. The contract is one of three composed into IFormField; the other two, IFormFieldAnnotationObject and IPdfDocumentObject, cover geometry and document identity respectively.

This interface matters because every concrete form field that IronPDF exposes inherits its data members from IFormFieldObject. TextFormField, CheckboxFormField, ComboboxFormField, RadioFormField, SignatureFormField, and ImageFormField all implement IFormField, which means they pick up the IFormFieldObject surface by inheritance. Code that reads field names, writes values, or audits form state can rely on these properties without casting to a concrete type.

The headline data members fall into three groups. For identity, read Name (the local field name) or FullName (the dotted, fully-qualified name); both are settable but FullName is usually the form-design identifier. For state, assign Value to fill a text, choice, or checkbox field, check ReadOnly first, and respect MaxLength for text fields. For type discovery, inspect FormType (string label) or Type (the PdfFormFieldType enum), and use Choices to enumerate valid options on combo-box and radio fields. Reading a name and writing a value on a loaded document is demonstrated in the edit PDF forms how-to.

using IronPdf;
using IronSoftware.Forms;

PdfDocument pdf = PdfDocument.FromFile("application.pdf");

// FindFormField returns IFormField, which inherits the IFormFieldObject surface.
IFormField field = pdf.Form.FindFormField("FullName");

if (field != null && !field.ReadOnly)
{
    // Identity, state, and type discovery, all from IFormFieldObject.
    string id = field.FullName;
    string kind = field.FormType;

    if (field.MaxLength == 0 || "Jane Doe".Length <= field.MaxLength)
    {
        field.Value = "Jane Doe";
    }
}

pdf.SaveAs("application-filled.pdf");

Splitting these data members onto a distinct contract lets IronPDF expose the same field-level surface across multiple consumer types without forcing every consumer to handle annotation geometry. For building fillable PDFs from scratch with these same data members, see the create PDF forms how-to.

Properties

Annotations

Form field annotations

Declaration

List<IFormFieldAnnotation> Annotations { get; }

Property Value

Type	Description
System.Collections.Generic.List<IFormFieldAnnotation>

Choices

Selection choices

Declaration

List<string> Choices { get; }

Property Value

Type	Description
System.Collections.Generic.List<System.String>

DefaultAppearance

Default appearance string

Declaration

string DefaultAppearance { get; }

Property Value

Type	Description
System.String

FormFlags

Form field flags

Declaration

PdfFormFieldFlags FormFlags { get; }

Property Value

Type	Description
PdfFormFieldFlags

FormType

Form type

Declaration

string FormType { get; }

Property Value

Type	Description
System.String

FullName

Fully qualified name

Declaration

string FullName { get; }

Property Value

Type	Description
System.String

MaxLength

Maximum number of characters which can be specified in the value

Declaration

int MaxLength { get; set; }

Property Value

Type	Description
System.Int32

Name

Partial name

Declaration

string Name { get; set; }

Property Value

Type	Description
System.String

ObjType

Object type

Declaration

string ObjType { get; }

Property Value

Type	Description
System.String

ReadOnly

True if read-only

Declaration

bool ReadOnly { get; set; }

Property Value

Type	Description
System.Boolean

RichText

Form value using rich text

Declaration

string RichText { get; set; }

Property Value

Type	Description
System.String

Type

Pdf form field type

Declaration

PdfFormFieldType Type { get; }

Property Value

Type	Description
PdfFormFieldType

Value

Form value

Declaration

string Value { get; set; }

Property Value

Type	Description
System.String

Inherited members

Client