Undoubtedly, creating multiple Word instances that you don't kill has choked your system(Hint: NewWordFile.Quit does not relate to Set NewDoc = CreateObject("word.application")). Your code has other issues, too.
Here's a more flexible approach that allows for the possibility that doesn't require knowing in advance which paragraphs contain your strings or, especially for the second string, how long it might be:
Sub Abrir()
Dim StrFldr As String, StrFlNm As Strin, WdObj As Object, WdDoc As Object, xlSht As Worksheet, r As Long
StrFldr = "C:\Users\njesus\Documents\Os meus documentos\": r = 1
Set WdObj = CreateObject("Word.Application"): WdObj.Visible = False
Set xlSht = ActiveSheet: xlSht.Range("A2:B" & Rows.Count).ClearContents
StrFlNm = Dir(StrFldr & "*.doc*")
Do While StrFlNm <> ""
r = r + 1
Set WdDoc = WdObj.Documents.Open(StrFldr & StrFlNm)
With WdDoc
With .Range
With .Find
.MatchWildcards = True
.Text = "N/O Ref[!\:]@:[!/]@/[! ]@>"
.Execute
End With
If .Find.Found Then xlSht.Range("A" & r).Value = Split(.Text, ":")(1)
End With
With .Range
With .Find
.MatchWildcards = True
.Text = "ASSUNTO:[!^13]@^13"
.Execute
End With
If .Find.Found Then xlSht.Range("B" & r).Value = Split(.Text, "ASSUNTO:")(1)
End With
.Close False
End With
StrFlNm = Dir()
Loop
Set WdDoc = Nothing: Set WdObj = Nothing: Set xlSht = Nothing
End Sub