Microsoft had no part in developing Pages, and coming from Word, you will immediately note that Pages is not a Word clone, or terribly portable document format. Although you can drag/drop a multi-page PDF onto a Pages document, only the first page will appear, and the remaining simply increase the size of the Pages document with no benefit. There is no means to transform that PDF object display into an Adobe PDF icon from within Pages. However...
If you have Adobe Acrobat Reader 11, or Adobe Acrobat Reader DC installed, you can right-click on the application icon, and click through Contents and Resources folders to get at the respective, but different PDF .icns icon files.
Reader 11 Reader DC

You can then option-drag (copy) the .icns file to your Desktop, and double-click it to open in Preview. The .icns file is a 225KB collection of different size individual icons that are either 144 dpi, or 72 dpi at different width x height. Once the .icns is open in Preview, I would select the third thumbnail (512 x 512 @ 144 dpi), and then export as full quality .jpeg (or PDF) to the Desktop. Then, you can simply drag/drop onto the open Pages document. This will add 78KB to the document.