How do I print two-sided?
Two-sided - or "duplex" - printing is a setting that must be defined at the computer at the time of printing. If your document is portrait-oriented (taller than it is wide), select flip/bind on long edge. Choose short edge for landscape-oriented documents.
The location of the two-sided printing option varies by software. Here are a few common examples...
Microsoft has a "Print on both sides" button just after you choose which pages to print:
Adobe has a "Print on both sides of paper" button just after the page fit / scaling options, with radio buttons to choose short or long edge binding:
Foxit Reader has a "Print on both sides of paper" button with flip on long / short edge radio buttons below it: