The .tax file can only be opened by the TurboTax software for the year of the tax data file.
For tax year 2018 and if you used the TurboTax online editions you can get the W-2 worksheets which have the tax data entered from the W-2. You have to use Print Center and request all the worksheets.
When you sign onto your online account and land on the Tax Home web page, scroll down and click on Add a state. See screenshot
This will take you back to the 2018 online tax return.
Click on Tax Tools on the left side of the online program screen. Then click on Print Center. Then click on Print, save or preview this year's return. Choose the option Include government and TurboTax worksheets