The tax data file which has a file extension of .tax2018 for tax year 2018 can only be opened by the TurboTax software for 2018 - https://turbotax.intuit.com/personal-taxes/cd-download/
Download the PDF of the 2018 tax return which can be opened by any compatible PDF viewer, such as Adobe Reader - https://get.adobe.com/reader/
To access your current or prior year online tax returns sign onto the TurboTax website with the userID you used to create the account - https://myturbotax.intuit.com/
Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on the Year and Click on Download/print return (PDF)
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