I don't see the problem with the data you posted but I did fix some of your code declarations and streamlined it which may have resolved the issue. Try this code with your real data and see if you still have the problem.
Code:
Sub ExWordPruebam2()
Dim wordapp As Object, objWord As Object
Dim fs As Object, documento As Object
Dim objselection As Object
Dim fila As Integer, i As Integer
Dim tema As String, nomprof As String, camino As String
Dim num As Integer, pts As Integer
Dim pregunta As String, opA As String, opB As String, opC As String, opD As String
Dim ans As String, respC As String, explRC As String, dif As String, ref As String
Dim obj As String, topic As String, pclave As String, prof As String
Set wordapp = CreateObject("Word.Application")
Set fs = CreateObject("Scripting.FileSystemObject")
Set documento = wordapp.Documents.Add
Set objselection = wordapp.Selection
tema = ActiveSheet.Cells(1, 2).Value
objselection.TypeText tema & vbCr
nomprof = ActiveSheet.Cells(6, 2).Value
objselection.TypeText nomprof & vbCr
Range("A8").Select
fila = Cells(Rows.Count, 1).End(xlUp).Row
wordapp.Visible = True
For i = 8 To fila
With ActiveSheet
num = .Cells(i, 1).Value
pregunta = .Cells(i, 2).Value
opA = .Cells(i, 3).Value
opB = .Cells(i, 4).Value
opC = .Cells(i, 5).Value
opD = .Cells(i, 6).Value
ans = .Cells(i, 7).Value
respC = .Cells(i, 8).Value
explRC = .Cells(i, 9).Value
pts = .Cells(i, 10).Value
dif = .Cells(i, 11).Value
ref = .Cells(i, 12).Value
obj = .Cells(i, 13).Value
topic = .Cells(i, 14).Value
pclave = .Cells(i, 15).Value
prof = .Cells(i, 16).Value
End With
With objselection
.TypeText num & vbCr
.TypeText pregunta & vbCr
.TypeText "a. " & opA & vbCr
.TypeText "b. " & opB & vbCr
.TypeText "c. " & opC & vbCr
.TypeText "d. " & opD & vbCr
.TypeText "ANS: " & ans & vbCr
.TypeText "Repuesta correcta " & vbCr
.TypeText respC & vbCr
.TypeText "Explicación de la respuesta " & vbCr
.TypeText explRC & vbCr
.TypeText "PTS: " & pts & vbCr
.TypeText "DIF: " & dif & vbCr
.TypeText "REF: " & ref & vbCr
.TypeText "OBJ: " & obj & vbCr
.TypeText "TOP: " & topic & vbCr
.TypeText "KEY: " & pclave & vbCr
.TypeText "NOT: " & prof
End With
Next i
With wordapp.ActiveDocument
camino = ThisWorkbook.Path & "\" & nomprof
.SaveAs Filename:=camino & ".rtf"
.Close savechanges:=True
End With
wordapp.Application.Quit
Set fs = Nothing
Set objselection = Nothing
Set documento = Nothing
Set wordapp = Nothing
End Sub