In Word, click Office Button (at the top left)->Word
Options->Proofing->Autocorrect Options->Smart Tags
Check "Label text with smart tags", then check the Measurement Converter
box.
Click OK all the way out, then type, e.g.
1 cm
followed by a space, or if necessary a paragraph mark.
Mouse over your text and you should see an "Information" icon (i in circle,
with a dropdown to the right. You may also see some blue underlining). If
you don't, wait a second or two as recognition is not necessarily
instantaneous. If you still don't see it, close and restart Word and try
entering the text again.
Once you see the dropdown you should be able to select one of the
conversions offered, which will then replace your text. You cn find out more
about what conversions are provided and how to define your own by clicking
the "About" option in the dropdown list.