Create a different header and/or footer for part of a document
See Nutshell at the bottom of page

When you create a header or footer, Word automatically uses the same header or footer throughout the entire document. To create a different header or footer for part of a document, divide the document into sections, and then break the connection between the header or footer in the current section and the previous one.

1. If you haven't done so already, insert a section break where you want to start a new section that contains a different header or footer.  
   1. Click where you want to insert a section break.
   2. On the Insert menu, click Break.
   3. Under Section break types; click the option that describes where you want the new section to begin.
2. Click in the section for which you want to create a different header or footer.
3. On the View menu, click Header and Footer.
4. If necessary, move to the header or footer you want to change.
   1. To view a header or footer, switch to print layout view. To edit or format a header or footer, you need to display the header or footer you want.  On the View menu, click Header and Footer.  
   2. To move to the header or footer you want, click a button on the Header and Footer toolbar.
   3. Make your changes to the header or footer.

Tip   In print layout view, you can quickly switch between the header or footer and the document text. Just double-click the dimmed header or footer or the dimmed document text.

5. On the Header and Footer toolbar, click Same as Previous .
6. Change the existing header or footer, or create a new one for this section.
   1. On the View menu, click Header and Footer. 
   2. To create a header, enter text or graphics in the header area. Or click a button on the Header and Footer toolbar.
   3. To create a footer, click Switch Between Header and Footer to move to the footer area. Then repeat step 2.
   4. When you finish, click Close.

Tip   The text or graphics you enter in a header or footer is automatically left aligned. You may want to center the item instead or include multiple items (for example, a left-aligned date and a right-aligned page number). To center an item, press TAB; to right align an item, press TAB twice.

7. To create a different header or footer for subsequent sections, repeat steps 1 through 6.

IN A NUTSHELL:  Open your saved letterhead—type your letter.  When your letter becomes 2 pages, go back to the end of the first page, Insert, Break, Section break:  Next page.  Go to page 2, View, Header and Footer, Page Setup, Check Different first page, Section start—NewPage, Apply to this section.  For subsequent pages:  Go to the end of the 2^nd to last page, Insert, Break, Section Break: Next page.