This configuration step for DRM is optional.

Adding a Previewer column to the document library will permit high-trust users to view documents in the browser. The Previewer column is safe for use by low-trust user groups as well, meaning that it can be added to a view of the document library that is used by both low- and high-trust user groups.

Instructions to add the Prizm Preview column to a document library are in the section Configuring the Previewer.