Summarize:

If your brochure is saved as a PDF on a Mac, Preview is most likely the default program with which the brochure will open, so just double-click the brochure. If the brochure doesn't open in Preview, click the brochure file, then click File, select Open With, and click Preview in the resulting menu. It's in the upper-left side of the screen. A drop-down menu will appear. This option is near the bottom of the drop-down menu. Doing so opens the "Print" window. Click the "Printer" drop-down box at the top of the window, then click the printer that you want to use. It resembles a sideways silhouette. Click the drop-down box that's below the "Orientation" section, click Layout, click the "Two-Sided" box, and click Long-Edge Binding. It's at the bottom of the window. Your brochure should print on both sides. If your printer doesn't support double-sided printing, you can print only the first page from your brochure, remove the paper, reinsert the paper printed-side-up and front cover-side-in, and then print only the second page.
Open the brochure in Preview. Click File. Click Print…. Select a printer. Click the "Horizontal" orientation option. Set up double-sided printing. Click Print.