public PdfAcroFormFieldAppearance Appearance { get; set; }

Public Property Appearance As PdfAcroFormFieldAppearance

using DevExpress.Pdf;

using (PdfDocumentProcessor processor = new PdfDocumentProcessor())
{
    // Load a document:
    processor.LoadDocument("..\\..\\Document.pdf");

    // Create a text box field:
    PdfAcroFormTextBoxField textBox =
         new PdfAcroFormTextBoxField("text box", 1, new PdfRectangle(230, 690, 280, 710));

    // Specify text box text and appearance:
    textBox.Text = "Text Box";
    textBox.Appearance.BackgroundColor = new PdfRGBColor(0.8, 0.5, 0.3);
    textBox.Appearance.FontSize = 12;

    // Create a radio group field:
    PdfAcroFormRadioGroupField radioGroup =
         PdfAcroFormField.CreateRadioGroup("Gender Group", 1);

    // Add the first radio button to the group and specify its location:
    radioGroup.AddButton("button1", new PdfRectangle(230, 635, 250, 655));

    // Add the second radio button to the group:
    radioGroup.AddButton("button2", new PdfRectangle(310, 635, 330, 655));

    // Specify radio group's selected index and appearance:
    radioGroup.SelectedIndex = 0;
    radioGroup.Appearance.BorderAppearance = new PdfAcroFormBorderAppearance()
    { Color = new PdfRGBColor(0.8, 0.5, 0.3), Width = 3 };

    // Add form fields to the page:
    processor.AddFormFields(textBox, radioGroup);

    // Save the resulting document:
    processor.SaveDocument("..\\..\\Result.pdf");
}

Imports DevExpress.Pdf

Namespace AddFormFieldsToExistingDocument
    Friend Class Program
        Shared Sub Main(ByVal args() As String)
            Using processor As New PdfDocumentProcessor()

                ' Load a document:
                processor.LoadDocument("..\..\Document.pdf")

                ' Create a text box field:
                Dim textBox As New PdfAcroFormTextBoxField("text box", 1, New PdfRectangle(230, 690, 280, 710))

                ' Specify text box text and appearance:
                textBox.Text = "Text Box"
                textBox.Appearance.BackgroundColor = New PdfRGBColor(0.8, 0.5, 0.3)
                textBox.Appearance.FontSize = 12

                ' Create a radio group field:
                Dim radioGroup As PdfAcroFormRadioGroupField = PdfAcroFormField.CreateRadioGroup("Gender Group", 1)

                ' Add the first radio button to the group and specify its location:
                radioGroup.AddButton("button1", New PdfRectangle(230, 635, 250, 655))

                ' Add the second radio button to the group:
                radioGroup.AddButton("button2", New PdfRectangle(310, 635, 330, 655))

                ' Specify radio group selected index and appearance:
                radioGroup.SelectedIndex = 0
                radioGroup.Appearance.BorderAppearance = New PdfAcroFormBorderAppearance() With {.Color = New PdfRGBColor(0.8, 0.5, 0.3), .Width = 3}

                ' Add form fields to the page:
                processor.AddFormFields(textBox, radioGroup)

                ' Save the resulting document:
                processor.SaveDocument("..\..\Result.pdf")
            End Using
        End Sub
    End Class
End Namespace