Are you saving the .tax20XX file or the .pdf file?
The .tax20XX file can only be opened with the TurboTax program for that year.
The .pdf can be opened on any device that has a pdf reader installed on it (which the majority of devices come with).
Do you still have the programs installed on the computer? If all you saved were the .tax20XX files, and you open the 2017 program you should be able to view the 2017 return, 2016 program you can view the 2016 return, etc.