Welcome to the Community, Peter.
The option to open two company files at the same time is only applicable if you're using different versions of QuickBooks Desktop (QBDT). If you're using QBDT Enterprise or QuickBooks Accountant, you can open a Secondary company file while still working on the Primary one.
There are 3 ways to open a Secondary file. While the first company file is open:
- Double-click the second company file's name.
- Double-click the QuickBooks icon.
- Go to the File menu, then select Open Second Company.
To learn about restrictions on both Primary and Secondary files, kindly visit: Open and use a secondary company file in QuickBooks Desktop.
Moreover, I'll also share this article that can serve as your reference if you want to learn how to issue a bill or check between your separate company files in QuickBooks: Create transactions between different company files in QuickBooks Desktop Enterprise.
Feel free to leave a reply if you have additional QuickBooks-related queries. The Community team always has your back. Have a good one.
