I believe, it depends on the printer you are using. But anyway you can use sendkeys method with key sequence appropriate to "your" MS Word version and to the printer you are using.

For my printer at the moment I can do the following to switch printing to both sides:

oWord=getOBJECT(,"Word.Application")
oWOrd.Application.Activate
oWord.Wordbasic.Sendkeys("%fp%p{down}", -1)
oWord=.null.

>I have next code for VFP-6 (Office2000):
>
>ox=createobject('word.document')
>ox.application.Documents.Open("mydoc.doc")
>ox.application.Activedocument.printout
>
>How I can switch printing one or two side document?
>
>Thanks.