There is only one file type that uses the .TAX17 extension:
TurboTax 2017 Tax Return File
A TAX17 file is a tax return created by Intuit TurboTax 2017, a program used to complete tax returns in the U.S. It contains state and federal tax forms and personal information entered by the user. TAX17 files are an alternative to the more popular .TAX2017 files that are saved by default by TurboTax 2017.
Updated: December 3, 2017