Until QuickBooks Online supports importing Purchase Orders from Excel or Text files then you could consider using one of the Data Import Utilities that you can find in the Intuit Apps Marketplace.
One of those apps is called Axis Online that I am involved in which can take Purchase Orders in a Excel file, Text or even and IIF file, upload and directly import into QuickBooks Online. It will save you considerable time over having to enter those manually.
I hope that gives you another option to consider.
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