I did everything how you wrote, the same error" Argument not optional" occurred on line . Just for information after that google it and find solution to change line
to this line
And everything work correctly, but it shows for all documents "no matches", although I checked in these documents there are suitable words. Just for note except adding "Word.Range" to line "Dim ORng" I did not do any changes in code and copy everything correctly.(Sorry for bad English and thanks in advance)