The printed purchase orders and transfers include a barcode to help you quickly find them from the main purchase order and transfer screens in the Back Office.
Once you have created your transfer or purchase order, click on the Print Purchase Order button:

A window will pop up, asking you what order you want the items on the printout to be displayed in, and whether or not you want to include cost prices:

This will open another tab in your browser that you can then print from.
To print right-click on the page and select 'Print..' selecting the printer you wish to print from.
Once you have the paper copy, you have a barcode to scan that corresponds to your Purchase Order number:

Now when you need to find the Purchase Order quickly you can navigate to the Purchase Order list, once on the list click into the Purchase Order number field, you can now scan the barcode from the printed Purchase Order:

You can now continue working on the purchase order as needed.