QuickBooks does not change your original Quicken file in any way. You can continue to use your original file with Quicken. There is no connection between your Quicken data and your new QuickBooks company. QuickBooks creates a new data file for you to use with QuickBooks.
You may want to continue using Quicken for personal finance and for investment accounts. Here are some personal finance activities you can perform only with Quicken:
Track investments: Quicken includes investment tracking and reporting. It reports on average annual total return, capital gains, and investment income.
Amortize mortgage loans: Each time you record a payment made on a loan, Quicken updates the dollar amount of payments made and calculates the amount credited to principal and interest.
Create reports for personal finances: Quicken has many preset reports designed for personal use.
Important: You can' t use online banking with the same account in both Quicken and QuickBooks. It will not work correctly. If you want to use online banking with the account in QuickBooks, stop using it with the account in Quicken. The same applies to online vendor payment: if you have the same account in Quicken and QuickBooks, use the service in one program only.