When you insert a page in a Word document, it is always underlined and the normal method cannot be cleared.
When you insert a header in a document, a horizontal line often appears below and cannot be removed by using the normal method, but you can try the following methods to resolve it.
1. Make sure the insertion point is in the header.
2. Select "format" → "borders and shading" to open the Borders and Shading dialog box.
3. Switch to the Borders tab and select None in the border setting.
4. Select paragraph in the Apply to Drop-down list, and click OK.