There is only one file type that uses the .TAX2013 extension:
TurboTax 2013 Tax Return
Tax return saved with TurboTax 2013, a U.S. tax preparation program; contains federal tax forms for the 2013 tax year along with data entered by the user; may also include state tax forms if a specific state version has been downloaded within TurboTax.
TAX2013 files can be created with the desktop version of TurboTax or exported from TurboTax Online. To create a TAX2013 file in TurboTax Online, click the "Save your 2013 return to your computer" link in the lower-left corner of the browser window. This option allows you to export a copy of the online return to your local disk that can be opened with TurboTax 2013.
Completed tax returns can be e-filed directly from the program. The completed forms can also be printed and mailed to the appropriate tax authorities. 2013 taxes are filed in 2014, so returns with a ".tax2013" extension are typically filed in 2014.
NOTE: TAX2013 files can be encrypted to protect personal financial data. If a tax return has been secured with a password, you will need the correct password in order to open the file.
Updated: May 19, 2017