Sub 甲烷下标()
'
' 甲烷下标 宏
'
'Selection.Find.ClearFormattingSelection.Find.Replacement.ClearFormattingWith Selection.Find.Text = "CH4".Replacement.Text = "CHguoshao4".Forward = True.Wrap = wdFindContinue.Format = False.MatchCase = False.MatchWholeWord = False.MatchByte = True.MatchWildcards = False.MatchSoundsLike = False.MatchAllWordForms = FalseEnd WithSelection.Find.Execute Replace:=wdReplaceAllSelection.Find.ClearFormattingSelection.Find.Replacement.ClearFormattingWith Selection.Find.Replacement.Font.Superscript = False.Subscript = TrueEnd WithWith Selection.Find.Text = "guoshao4".Replacement.Text = "4".Forward = True.Wrap = wdFindContinue.Format = True.MatchCase = False.MatchWholeWord = False.MatchByte = True.MatchWildcards = False.MatchSoundsLike = False.MatchAllWordForms = FalseEnd WithSelection.Find.Execute Replace:=wdReplaceAll
End Sub

思路是将CH4替换为CH和一个特殊的文字，然后将这个特殊的文字，替换为下标的4。PS：CH4中的CH忽略大小写，均会被替换为大写的CH。