Here are the steps to create a custom border in Microsoft Word:

1. Open Word and click on the Design tab.
2. Under Page Layout, click Page Borders.
3. Click Page Border in the Borders and Shading window.
4. Select the Custom option from the list of choices.
5. Choose the color, style and width of your page border in Word.
6. Click OK to apply the border.

You can also add a border around text or images by selecting the content, clicking the "Home" tab and clicking the arrow next to the border icon. Then click "Borders and Shading..." and select a border setting, style, and page application. Finally, click "OK" .