You can determine the paper size to be edited on, and how much margin is left around the paper by using Page Setup.
1. Click File > Page Setup or Page Layout > Page Setup.
2. In the Page Setup dialog box, select the Paper tab and click the arrow of the Type list under Paper Size.
3. Select desired paper type such as Letter. Set the margins of the selected paper size.
4. You can change the units by clicking on the arrow buttons.
5. On Margins tab, you can set the sizes for each margin.
5. Click OK to save changes.
Page Setup > Margins > Apply to suggests settings for the section number, pointer position, and block setting of the active document. In most cases, you can select among This Section, This Point Forward, or Whole Document.
This Section is only available at the current document which has two or more sections. On selecting it, the selected page setup will apply to the current section where the pointer is located.
On selecting This Point Forward, the selected page setup will apply from the new section or page.
On selecting Whole Document, the selected page setup will apply to the entire document even if the active document is divided into two or more sections.