public abstract class PdfFormFieldFacade :
    IEnumerable<PdfWidgetFacade>,
    IEnumerable

Public MustInherit Class PdfFormFieldFacade
    Implements IEnumerable(Of PdfWidgetFacade),
               IEnumerable

using (PdfDocumentProcessor pdfDocumentProcessor = new PdfDocumentProcessor())
{
    pdfDocumentProcessor.LoadDocument("Documents//FormDemo.pdf");

    PdfDocumentFacade documentFacade = pdfDocumentProcessor.DocumentFacade;
    PdfAcroFormFacade acroForm = documentFacade.AcroForm;

    //Change all form fields' color settings:
    var fields = acroForm.GetFields();
    foreach (PdfFormFieldFacade field in fields)
    {
        ChangeFormFieldColor(field);
    }
}
  private static void ChangeFormFieldColor(PdfFormFieldFacade field)
  {
      foreach (PdfWidgetFacade pdfWidget in field)
      {
          //Change color and border settings
          //for all form fields:
          pdfWidget.BorderWidth = 1;
          pdfWidget.BackgroundColor = new PdfRGBColor(0.81, 0.81, 0.81);
          pdfWidget.BorderColor = new PdfRGBColor(0.47, 0.44, 0.67);
          pdfWidget.FontColor = new PdfRGBColor(0.34, 0.25, 0.36);

          //Change border style for text form fields:
          if (field.Type == PdfFormFieldType.Text)
          {
              pdfWidget.BorderStyle = PdfBorderStyle.Underline;
          }
      }
  }

Using pdfDocumentProcessor As New PdfDocumentProcessor()
  pdfDocumentProcessor.LoadDocument("Documents//FormDemo.pdf")

  Dim documentFacade As PdfDocumentFacade = pdfDocumentProcessor.DocumentFacade
  Dim acroForm As PdfAcroFormFacade = documentFacade.AcroForm

  'Change all form fields' color settings:
  Dim fields = acroForm.GetFields()
  For Each field As PdfFormFieldFacade In fields
    ChangeFormFieldColor(field)
  Next field
End Using
  private static void ChangeFormFieldColor(PdfFormFieldFacade field)
    For Each pdfWidget As PdfWidgetFacade In field
      'Change color and border settings
      'for all form fields:
      pdfWidget.BorderWidth = 1
      pdfWidget.BackgroundColor = New PdfRGBColor(0.81, 0.81, 0.81)
      pdfWidget.BorderColor = New PdfRGBColor(0.47, 0.44, 0.67)
      pdfWidget.FontColor = New PdfRGBColor(0.34, 0.25, 0.36)

      'Change border style for text form fields:
      If field.Type = PdfFormFieldType.Text Then
        pdfWidget.BorderStyle = PdfBorderStyle.Underline
      End If
    Next pdfWidget