I had created a rather long explanation of the default paper size and then foolishly hit the wrong button. Now that dissertation is somewhere in Hyperworld.

To recap, the default page size was originally defined by the location/language chosen by the user when the computer was first turned on. This setting is in the International preference pane.

Now it seems that this is controlled by whatever setting the users chooses in the Print & Fax (Print & Scan) preference pane.
Is this where he is changing the paper size or is he changing it inside Word?

A document that was created in A4 size in Word will always open as A4 size unless it has been changed and saved again as US Letter.

This from Word Help:
On the Format menu, click Document.
Click Page Setup.
On the Paper Size pop-up menu, select a paper size.
Click OK.
On the Apply to pop-up menu, click Whole document, and then click OK.

Could the first round be a draw?

Merry Christmas