Add content to a existent rtf file from RichTextBox - (VB.NET 2015)

[CM16]

Hi. Thanks for your attention. I need to save the Richtextbox content on a existent rtf file (whit data).
I need that the file accumulates data.
I am using the next code, but this overrides the file existent.

Dim CarpetaUsuario As String = CapetaLogs & "\" & ppSuUsuario
Dim NombreArchivo As String = CarpetaUsuario & "\" & Format(Now, "yyMMdd") & ".rtf"

If Not Directory.Exists(CarpetaUsuario) Then
My.Computer.FileSystem.CreateDirectory(CarpetaUsuario)
End If

rtb_chat.SaveFile(NombreArchivo, RichTextBoxStreamType.RichText)

Continue reading...