If it's just an image, select it, click the Rotate button in the Arrange group
on the Picture Tools ribbon, and choose Flip Horizontal.
If it's a whole page including text, then Word can't do it by itself. You have a
couple of options:
- In the Print dialog, click the Properties button to get to the dialog that's
provided by the printer driver (it's different for each printer). Look for a
check box, radio button, or dropdown that mentions "t-shirt" or "transfer" or
"mirror image". If it's there, that's the quickest way.
- Make up the page in PowerPoint. Select it, cut it to the clipboard, and then
Paste Special as one of the graphics-type objects (PNG, JPG, etc.). Then click
Arrange > Rotate > Flip Horizontal. You can print it from PowerPoint, or copy it
and paste it into a Word document.