Tap to turn on Border, then use the controls to choose a border style, color, and width.
To change the transparency, drag the Opacity slider at the bottom of the controls.
To move the border behind all the objects on the page, tap Arrange, then drag the slider all the way to the left.
If your document is a word-processing document, tap Text Wrap, then tap None; or turn off Move with Text.
To lock the border so it doesn’t get moved accidentally, tap Arrange (at the top of the controls), then tap Lock.
When you’re finished, tap anywhere on the page to dismiss the controls.
To learn how to set your border as a section layout object so it appears on every page, see Add a border to an object in Pages on iPad