The QuickBooks portable files can only be opened in QuickBooks Desktop. Also, there isn't a direct way to port it over to the Online version.
I can share a way to help you import the data from the portable file to QuickBooks Online.
You'll want to use a trial version of QuickBooks Desktop. Depending on where the portable file was originally opened, you can get the trial versions from this article: Download a trial of QuickBooks Desktop.
If you need help installing your QuickBooks Desktop trial copy, you can use this article for a guide: Install QuickBooks Desktop.
After installing, you can open the portable file from QuickBooks Desktop. Here's how to do it:
Go to the File menu and choose Open or Restore Company.
Ready to work on your QuickBooks Online company file after migrating? Check out the guides and tutorials in our articles list page. I'm certain they can help you in managing your books, recording transactions and such.
I'll ensure you're able to work on your QuickBooks Online company file smoothly. Please let me know if you have any other questions. I'm here to help.