How do I print or convert a .tax file?

The only way to print a .taxyyyy file is to open it in the TurboTax desktop software for the corresponding year. If you do not have the software you could try using the TaxPrinter service. You send them your .tax file and they send you back a PDF of the tax return, which you can then print with Acrobat Reader. TaxPrinter has no connection with TurboTax. I have never used TaxPrinter, so I cannot make a recommendation. I'm just making you aware of it.

I don't know what you mean by "convert." What would you want to convert the .tax file to? If you mean that you want to convert it to a PDF, that's the same as printing.