To reveal a document to all deposition participants, first select a document from the document panel on the left.

Selecting a document will enable the "Reveal Document" button in the document controls. Click this button to reveal the document.

When you reveal a document, the participants will see this:

At this point, every participant can navigate through the pages of the document you just revealed. However, you do not need to wait for the witness to select the document. You can control the witness' screen from the deposition control panel.