If the files end in .tax or .tax2014 etc. you need each year's program installed on a full Windows or Mac computer to open them. Or You can download the pdf files from Online to open them on your iPad or anywhere.
If you can't get the pdf files and only have the .tax files......You could try the TaxPrinter service (not connected with Turbo Tax) to convert a .tax file to pdf at
http://www.taxprinter.com