QuickBooks Desktop's integrated features make managing your business finances a breeze. For those moments when there's something it doesn't do that you'd like or need it to, there are third-party apps that can help you connect to other services.
I invite other users in the community to chime in with what they use. You can also check out our apps list to see what's available. I've gotten you started by throwing "purchase order" in the search bar on our Apps for QuickBooks Desktop website and got these results. The one thing to keep in mind when searching our site is some of these apps may only be available for US versions of QuickBooks Desktop. The best way to make sure they'll work with your version of the program is to contact the app's support team. Clicking the name of the app will bring you to their information page, where you can see the Policy and Support options among other details.
Best of luck finding something that works for you and your business!