Here is a full code that I used:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Cursor.Current = Cursors.WaitCursor
Dim filename As String = Application.StartupPath + "\\Doc1.doc"
Dim doc As Document = New Document(filename)
builder = New DocumentBuilder(doc)
AddHandler doc.MailMerge.MergeField, AddressOf HandleMergeField
' --- the following code is for MailMerge without database
' --- substitute it with your code
Dim sr As StreamReader = File.OpenText(Application.StartupPath + "\InsertHtml.txt")
Dim htmltext As String = sr.ReadToEnd()
sr.Close()
Dim fields(1) As String
fields(0) = "h1"
fields(1) = "h2"
Dim values(1) As String
values(0) = htmltext
values(1) = htmltext
doc.MailMerge.Execute(fields, values)
' --- end of MailMerge process
doc.Save(System.IO.Path.GetFileNameWithoutExtension(filename) + "_modified.doc")
Cursor.Current = Cursors.Default
End Sub
Private builder As DocumentBuilder
Private Sub HandleMergeField(ByVal sender As Object, ByVal e As Aspose.Word.Reporting.MergeFieldEventArgs)
If (e.DocumentFieldName.StartsWith("h")) Then
builder.MoveToMergeField(e.DocumentFieldName)
builder.InsertHtml(e.FieldValue)
End If
End Sub
Test files in attachment