How can I open a 2006 TurboTax file which was not saved as a pdf?

You would have to have the 2006 program. You can find it online if you Google it. 

2006?  TurboTax does not support a tax return that old.  TurboTax supports tax years 2020 thru 2017.

For a fee you could use the service provided by http://www.taxprinter.com/

If you have old .tax files you can try converting them to pdf files at  Www.Taxprinter.Com 

It might be expensive.  They are not connected with Turbo Tax.  Use it at your own risk.

Even if you could find the 2006 software, it would be useless without the form updates that are no longer available.    You also might not be able to find an old computer operating system that could even load 2006.