First go to their Page, click on the gear under the cover photo, and select Like as Your Page (the Like button is for you as a person). Then go back to your Page, start writing your post, type the @ symbol and the Page name, and it should appear as a link.
This creates a direct link between your Page and their Page. It’s cross promotion and creates goodwill. They will also appear in the box called Likes on your Page. This Like box shows businesses you recommend and want others to know about. If you want to tag the Page but don’t want them to stay in that coveted real estate, you can like them for the post then unlike them and they will not be featured in your Like box.