The Share & Print buttons let you export the pdf you're currently viewing to other pdf-reader apps on your device, as well as wirelessly print. This will include any annotations you have made on that pdf too!
1. Choose "Share PDF" from the PDF options menu
Open the PDF options menu and select the "Share" button
Share the PDF to another app on the device
Once the app has rendered a PDF file, you will see a menu of any pdf-reading app on your device that is able to be shared to.
2. Choose "Print PDF" from the PDF options menu
Print wirelessly to your printer
Once the app has rendered a PDF file, you can wirelessly print to a printer, and even save to Google Print via Cloud Print