Read PDF interactive form fields in C# and VB.NET

GemBox.Pdf supports reading PDF interactive form fields.

An interactive form in GemBox.Pdf is represented by a PdfInteractiveForm class and can be accessed via the Form property of the PdfDocument class. The base class of all PDF fields is a PdfField and can be accessed via the Fields property of the PdfInteractiveForm class.

The following example shows how you can read all PDF interactive form fields, their type, name, value, and other properties, in a PDF document.

Screenshot of PDF interactive form fields read with GemBox.Pdf

C#
VB.NET

View on GitHub

using System;
using System.Globalization;
using System.IO;
using System.Linq;
using GemBox.Pdf;
using GemBox.Pdf.Forms;

class Program
{
    static void Main()
    {
        // If using the Professional version, put your serial key below.
        ComponentInfo.SetLicense("FREE-LIMITED-KEY");

        var writer = new StringWriter(CultureInfo.InvariantCulture);
        string format = "{0,-16}|{1,20}|{2,-20}|{3,-20}|{4,-20}", separator = new string('-', 100);

        // Write the header.
        writer.WriteLine("Document contains the following form fields:");
        writer.WriteLine();
        writer.WriteLine(format,
            "Type",
            '"' + "Name" + '"',
            "Value",
            "ExportValue/Choice",
            "Checked/Selected");
        writer.WriteLine(separator);

        PdfFieldType? fieldType;
        string fieldName, fieldExportValueOrChoice;
        object fieldValue;
        bool? fieldCheckedOrSelected;

        using (var document = PdfDocument.Load("%InputFileName%"))
            // Group fields by name because all fields with the same name are actually different representations (widget annotations) of the same field.
            // Radio button fields are usually grouped. Other field types are rarely grouped.
            foreach (var fieldGroup in document.Form.Fields.GroupBy(field => field.Name))
            {
                var field = fieldGroup.First();

                fieldType = field.FieldType;
                fieldName = '"' + field.Name + '"';
                fieldValue = field.Value;

                foreach (var widgetField in fieldGroup)
                {
                    switch (widgetField.FieldType)
                    {
                        case PdfFieldType.CheckBox:
                        case PdfFieldType.RadioButton:
                            // Check box and radio button are toggle button fields.
                            var toggleField = (PdfToggleButtonField)widgetField;

                            fieldExportValueOrChoice = toggleField.FieldType == PdfFieldType.CheckBox ?
                                    ((PdfCheckBoxField)toggleField).ExportValue :
                                    ((PdfRadioButtonField)toggleField).Choice;
                            fieldCheckedOrSelected = toggleField.Checked;

                            writer.WriteLine(format,
                                fieldType,
                                fieldName,
                                fieldValue,
                                fieldExportValueOrChoice,
                                fieldCheckedOrSelected);
                            break;

                        case PdfFieldType.ListBox:
                        case PdfFieldType.Dropdown:
                            // List box and drop-down are choice fields.
                            var choiceField = (PdfChoiceField)widgetField;

                            // List box can have multiple values if multiple selection is enabled.
                            if (fieldValue is string[] fieldValues)
                                fieldValue = string.Join(", ", fieldValues);

                            for (int itemIndex = 0; itemIndex < choiceField.Items.Count; ++itemIndex)
                            {
                                fieldExportValueOrChoice = choiceField.Items[itemIndex].ExportValue ?? choiceField.Items[itemIndex].Value;
                                fieldCheckedOrSelected = choiceField.FieldType == PdfFieldType.ListBox ?
                                        ((PdfListBoxField)choiceField).SelectedIndices.Contains(itemIndex) :
                                        ((PdfDropdownField)choiceField).SelectedIndex == itemIndex;

                                writer.WriteLine(format,
                                fieldType,
                                fieldName,
                                fieldValue,
                                fieldExportValueOrChoice,
                                fieldCheckedOrSelected);

                                // Write the field type, field name, and field value just once for a field group.
                                fieldType = null;
                                fieldName = null;
                                fieldValue = null;
                            }
                            break;

                        default:
                            // Text field may contain multiple lines of text, if enabled.
                            if (widgetField.FieldType == PdfFieldType.Text && ((PdfTextField)widgetField).MultiLine && fieldValue != null)
                                fieldValue = ((string)fieldValue).Replace("\r", "\\r");

                            fieldExportValueOrChoice = null;
                            fieldCheckedOrSelected = null;

                            writer.WriteLine(format,
                                fieldType,
                                fieldName,
                                fieldValue,
                                fieldExportValueOrChoice,
                                fieldCheckedOrSelected);
                            break;
                    }

                    // Write the field type, field name, and field value just once for a field group.
                    fieldType = null;
                    fieldName = null;
                    fieldValue = null;
                }

                writer.WriteLine(separator);
            }

        Console.Write(writer.ToString());
    }
}

Imports System
Imports System.Globalization
Imports System.IO
Imports System.Linq
Imports GemBox.Pdf
Imports GemBox.Pdf.Forms

Module Program

    Sub Main()

        ' If using the Professional version, put your serial key below.
        ComponentInfo.SetLicense("FREE-LIMITED-KEY")

        Dim writer = New StringWriter(CultureInfo.InvariantCulture)
        Dim format As String = "{0,-16}|{1,20}|{2,-20}|{3,-20}|{4,-20}", separator As String = New String("-"c, 100)

        ' Write the header.
        writer.WriteLine("Document contains the following form fields:")
        writer.WriteLine()
        writer.WriteLine(format,
            "Type",
            """"c & "Name" & """"c,
            "Value",
            "ExportValue/Choice",
            "Checked/Selected")
        writer.WriteLine(separator)

        Dim fieldType As PdfFieldType?
        Dim fieldName, fieldExportValueOrChoice As String
        Dim fieldValue As Object
        Dim fieldCheckedOrSelected As Boolean?

        Using document = PdfDocument.Load("%InputFileName%")
            ' Group fields by name because all fields with the same name are actually different representations (widget annotations) of the same field.
            ' Radio button fields are usually grouped. Other field types are rarely grouped.
            For Each fieldGroup In document.Form.Fields.GroupBy(Function(field) field.Name)

                Dim field = fieldGroup.First()

                fieldType = field.FieldType
                fieldName = """"c + field.Name + """"c
                fieldValue = field.Value

                For Each widgetField In fieldGroup

                    Select Case widgetField.FieldType

                        Case PdfFieldType.CheckBox,
                             PdfFieldType.RadioButton
                            ' Check box and radio button are toggle button fields.
                            Dim toggleField = CType(widgetField, PdfToggleButtonField)

                            fieldExportValueOrChoice = If(toggleField.FieldType = PdfFieldType.CheckBox,
                                CType(toggleField, PdfCheckBoxField).ExportValue,
                                CType(toggleField, PdfRadioButtonField).Choice)
                            fieldCheckedOrSelected = toggleField.Checked

                            writer.WriteLine(format,
                                fieldType,
                                fieldName,
                                fieldValue,
                                fieldExportValueOrChoice,
                                fieldCheckedOrSelected)


                        Case PdfFieldType.ListBox,
                             PdfFieldType.Dropdown
                            ' List box and drop-down are choice fields.
                            Dim choiceField = CType(widgetField, PdfChoiceField)

                            ' List box can have multiple values if multiple selection is enabled.
                            Dim fieldValues = TryCast(fieldValue, String())
                            If fieldValues IsNot Nothing Then fieldValue = String.Join(", ", fieldValues)

                            For itemIndex As Integer = 0 To choiceField.Items.Count - 1

                                fieldExportValueOrChoice = If(choiceField.Items(itemIndex).ExportValue, choiceField.Items(itemIndex).Value)
                                fieldCheckedOrSelected = If(choiceField.FieldType = PdfFieldType.ListBox,
                                    CType(choiceField, PdfListBoxField).SelectedIndices.Contains(itemIndex),
                                    CType(choiceField, PdfDropdownField).SelectedIndex = itemIndex)

                                writer.WriteLine(format,
                                    fieldType,
                                    fieldName,
                                    fieldValue,
                                    fieldExportValueOrChoice,
                                    fieldCheckedOrSelected)

                                ' Write the field type, field name, and field value just once for a field group.
                                fieldType = Nothing
                                fieldName = Nothing
                                fieldValue = Nothing
                            Next


                        Case Else
                            ' Text field may contain multiple lines of text, if enabled.
                            If widgetField.FieldType = PdfFieldType.Text AndAlso (CType(widgetField, PdfTextField)).MultiLine AndAlso fieldValue IsNot Nothing Then fieldValue = (CStr(fieldValue)).Replace(vbCr, "\r")

                            fieldExportValueOrChoice = Nothing
                            fieldCheckedOrSelected = Nothing

                            writer.WriteLine(format,
                                fieldType,
                                fieldName,
                                fieldValue,
                                fieldExportValueOrChoice,
                                fieldCheckedOrSelected)

                    End Select

                    ' Write the field type, field name, and field value just once for a field group.
                    fieldType = Nothing
                    fieldName = Nothing
                    fieldValue = Nothing
                Next

                writer.WriteLine(separator)
            Next
        End Using

        Console.Write(writer.ToString())
    End Sub
End Module

Next steps

GemBox.Pdf is a .NET component that enables developers to read, merge and split PDF files or execute low-level object manipulations from .NET applications in a simple and efficient way.

Download Buy

Published: February 19, 2019 | Modified: September 8, 2021 | Author: Stipo Rubić

Read PDF interactive form fields in C# and VB.NET

See also

Next steps