There doesn't appear to be anything 'wrong' with your code, but I can't see any point to the loop, either - you could do the same with:
Code:
With ActiveDocument.Range.Find
.ClearFormatting
.Replacement.ClearFormatting
.Text = "Trizol"
.Replacement.Text = "TRIzolŪ"
.Forward = True
.Format = False
.MatchCase = False
.Wrap = wdFindContinue
.MatchWholeWord = True
.Execute Replace:=wdReplaceAll
End With