using DevExpress.XtraRichEdit;
using DevExpress.XtraRichEdit.API.Native;
using System.Drawing;

using (var wordProcessor = new RichEditDocumentServer()) {
    Document document = wordProcessor.Document;
    foreach (Field field in document.Fields) {
        string strResult = document.GetText(field.ResultRange);

        if (strResult == "") {
            document.InsertText(field.ResultRange.Start, "Empty Value!");
        }
    }
} 

``Imports DevExpress.XtraRichEdit
Imports DevExpress.XtraRichEdit.API.Native
Imports System.Drawing

Using wordProcessor = New RichEditDocumentServer()
    Dim document As Document = wordProcessor.Document
    For Each field As Field In document.Fields
        Dim strResult As String = document.GetText(field.ResultRange)

        If strResult = "" Then
            document.InsertText(field.ResultRange.Start, "Empty Value!")
        End If
    Next field
End Using

winforms-richedit-document-api/CS/RichEditAPISample/CodeExamples/Export.cs#L109

options.AllowExtendingDocumentRange = false;
foreach (Paragraph par in document.Paragraphs.Get(item.ResultRange)) {
    plainText += document.GetText(par.Range, options);

winforms-richedit-document-api/VB/RichEditAPISample/CodeExamples/Export.vb#L97

options.AllowExtendingDocumentRange = False
For Each par As DevExpress.XtraRichEdit.API.Native.Paragraph In document.Paragraphs.[Get](item.ResultRange)
    plainText += document.GetText(par.Range, options)