Using C# PDF SDK
C# PDF Reader: How to read, extract field data from AcroForms in PDF file

String inputFilePath = Program.RootPath + "\\" + "1_AF.pdf";

List<BaseFormField> fields = PDFFormHandler.GetFormFields(inputFilePath);
Console.WriteLine("Number of Fields: " + fields.Count);
if (fields.Count > 0)
{
    foreach (BaseFormField field in fields)
    {
        Console.WriteLine("Field");
        Console.WriteLine("  Name:     " + field.Name);
        Console.WriteLine("  Visible:  " + field.IsVisible);
        Console.WriteLine("  Page:     " + field.PageIndex);
        Console.WriteLine("  Position: " + field.Position.ToString());
        Console.WriteLine("  Size: " + field.Size.ToString());
    }
}