Also, @LKMLI , here is the link to the first post in this thread about Transaction Pro Importer, a great third party app that I have used with great success.  I'm not sure if it's an app you're looking for to import transactions from a .xlsx or .csv spreadsheet, or if you're looking for the actual purchase order system itself which will then be importable into QB.

With the app I mentioned, as long as you can export a report to an Excel of CSV format from your external software, you can use Transaction Pro Importer to import into your Purchase Orders inside QB.  It is simply a matter of mapping fields in TPI that will coincide with your items in QB.  Once you get it working for you (after testing in a Sample file to make sure you are getting the results you require), it's a wonderful thing.

https://quickbooks.intuit.com/community/3rd-Party-apps/Transaction-Pro-Importer-a-Great-3rd-Party-Ap...

Good luck!