Why do you need to open a 2018 tax return file ending in .tax2018? Sorry you can’t install old programs. They only support the last 3 years. If you can’t download or open the pdf file and only have the data file ending in .tax20yy you could try the TaxPrinter service (not connected with Turbo Tax) to convert a .tax file to pdf at
http://www.taxprinter.com
OR get a copy from the IRS -
http://www.irs.gov/Individuals/Get-Transcript
Even if you install or reinstall 2018 or prior from a CD you will not be able to update the program or download any state programs you need. So you might not be able to even open the .tax2018 tax file. And since you can’t update the program your return might not be the same as you filed.
