Word doesn't have anything specific for this, but your printer might.
In the File > Print dialog, click the Properties button next to the
name of the printer. The dialog you get next is supplied by the
printer driver software, not by Word itself (so it's different for
each printer manufacturer and model). Somewhere in that dialog you may
find a setting for "mirror image" or "t-shirt printing" or something
like that.

For example, in my Canon printer's dialog, the dropdown labeled Media
has an entry for "T-Shirt Transfer". But for my Epson printer I have
to click the Advanced button, choose the "Flip Horizontal" option, and
change it from Off to On.

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Regards,
Jay Freedman
Microsoft Word MVP        FAQ: http://www.mvps.org/word