Attach form 4868 prepared by another CPA?

A Form 4868, Application for Automatic Extension of Time to File U.S. Individual Income Tax Return is not attached to a federal tax return.  The IRS already knows that an extension request was made based on the SSN you entered on the federal tax return and on the Form 4868.

What do you mean by "another CPA"? Are you a CPA? You cannot use TurboTax to prepare tax returns for clients. TurboTax is only for do-it-yourself consumer use and cannot be used by paid preparers. Intuit (the company that makes TurboTax) has three tax software product lines for professional preparers: ProSeries, Lacerte, and ProConnect. You can find information about all three product lines at the following link.

Professional tax software for preparers