Set the default paper size
1. On the Format menu, click Document.
2. Click Page Setup.
3. Select a paper size from the Paper Size pop-up menu, and then click OK.
4. Click Default, and then click Yes.
Note Setting the default paper size changes the page size for the template the current document was based on. If the current document is based on the Normal template and you change the default paper size, this change affects all new documents based on the Normal template. If the current document is based on a template other than the Normal template, only documents based on this template inherit the new page size.