System.Object
   System.Collections.ObjectModel.Collection<T>
      Xfinium.Pdf.Forms.PdfCalculatedFieldCollection
      Xfinium.Pdf.Forms.PdfFieldCollection
      Xfinium.Pdf.Forms.PdfFieldWidgetCollection
      Xfinium.Pdf.Forms.PdfListItemCollection
   Xfinium.Pdf.Annotations.PdfAnnotation
      Xfinium.Pdf.Forms.PdfFieldWidget
         Xfinium.Pdf.Forms.PdfCheckWidget
            Xfinium.Pdf.Forms.PdfCheckBoxWidget
            Xfinium.Pdf.Forms.PdfRadioButtonWidget
         Xfinium.Pdf.Forms.PdfComboBoxWidget
         Xfinium.Pdf.Forms.PdfListBoxWidget
         Xfinium.Pdf.Forms.PdfPushButtonWidget
         Xfinium.Pdf.Forms.PdfSignatureWidget
         Xfinium.Pdf.Forms.PdfTextBoxWidget
   Xfinium.Pdf.Forms.PdfField
      Xfinium.Pdf.Forms.PdfCheckBoxField
      Xfinium.Pdf.Forms.PdfListField
         Xfinium.Pdf.Forms.PdfComboBoxField
         Xfinium.Pdf.Forms.PdfListBoxField
      Xfinium.Pdf.Forms.PdfPushButtonField
      Xfinium.Pdf.Forms.PdfRadioButtonField
      Xfinium.Pdf.Forms.PdfSignatureField
      Xfinium.Pdf.Forms.PdfTextBoxField
   Xfinium.Pdf.Forms.PdfForm
   Xfinium.Pdf.Forms.PdfListItem
   Xfinium.Pdf.Forms.PdfSignatureLockFieldAction

Reference

XFINIUM.PDF Library