For documents with headers and other advanced formatting, such as forms, you should try using Microsoft Publisher instead. I use Publisher every day for documents and more, but use Word very occasionally. Publisher automatically opens to a document template selection, and I use many templates, but my most common is the 11 x 8.5. With Publisher, unlike Word, you can draw text boxes for headers and body text, as well as picture placeholders and other graphics. With Publisher, when the document is opened, there is no cursor automatically blinking. Even if you draw a text box in Word for text, Word's cursor is automatically at the top of the document, not in the text box. For advanced forms, I recommend Microsoft InfoPath, which allows you to use automated checkboxes, option buttons, buttons, picture buttons, and more. Together, Microsoft Publisher and Microsoft InfoPath make a great replacement for Microsoft Word.

Check your margins. That typically has settings for where page headers start and where the main body starts and you need to allow room for the size of your page headers, especially if larger text or more than 1 line headers.