In Pages, your only control over dpi is the quality of images that you use. Shapes and Text boxes (transparent) are confined to 72 dpi. And until Apple wakes up and builds print selection into the Print dialog, you are forced to use the clipboard to extract your work Pages.
Affinity Designer, and Affinity Photo are currently in the OS X App Store with Apple Design Awards. Affinity Publisher (DTP focus) is planned for next year. These applications will all share the same document architecture so that you can start something in Designer, and from its menu, switch to Photo for its strengths, then back to Designer again. Publisher, when available will share access to the other two applications for a complete DTP solution.
Here is a link to an Affinity Designer trial. There is no PDF manual, but there is comprehension in the Help menu and tutorials.
Affinity Designer lets you specifiy that your end work is 300 DPI in the CMYK color space. The 18 shapes, text, text on a curve, and images (providing they are 300 dpi) will result in a press-ready 300 dpi PDF export. You can choose to export your selection, or the entire page.