There are two ways to do this. 

Option 1 - Go to the Attachments tab of your PO in B2P, where a .pdf of your PO is available.

Option 2 - Navigate to your PO document and select View/Print PO from the drop-down menu under 'Purchase Order'.  This will open the PO in a new browser tab.  To print, use your mouse to right-click and select print.  From here, choose your destination, which can be a printer or .pdf.  Tip: Use the print menu settings to hide headers and footers (e.g. url, date, etc).

NOTE: If you would rather have a .pdf of your PO automatically sent to an email address you specify as soon as it is approved, please see the Adding a Non-Catalog Item to a Cart.