If you change the aspect ratio, you will be stretching the image in one
direction or the other.
If you're displaying images as they were originally created and they look
stretched, it's because your display settings are not correct for the
widescreen monitor. Standard displays have settings in the ratio 4:3,
widescreens in the neighborhood of 16:9. This is a function of Windows, not
Office.
How can I change the aspect ratio of photos/documents to view them
unstreched
on a wide screen?