The PDF file is necessary if you want to "look" at your return in the future, when the TT program for that year is no longer available. The .tax file is what's transferred from the previous year's TT program, into the current year's TT program. You can only open a .tax file with the appropriate year's version of the TT program that tax file is for. You can open and view a PDF with the adobe reader on any computer platform.
