Sub InsertTextFiles()
Application.ScreenUpdating = False
Dim strFolder As String, strFile As String, strTxt As String
strFolder = GetFolder
If strFolder = "" Then Exit Sub
strFile = Dir(strFolder & "\*.txt", vbNormal)
While strFile <> ""
    Open strFolder & "\" & strFile For Input As #1
    strTxt = Input(LOF(1), 1)
    Close #1
    ActiveDocument.Range.InsertAfter vbCr & strTxt
    strFile = Dir()
Wend
Application.ScreenUpdating = True
End Sub
 
Function GetFolder() As String
Dim oFolder As Object
Set oFolder = CreateObject("Shell.Application").BrowseForFolder(0, "Choose a folder", 0)
If (Not oFolder Is Nothing) Then
  GetFolder = oFolder.Items.Item.Path
Else
  GetFolder = ""
End If
Set oFolder = Nothing
End Function