What do you mean by "additional"?
If you have already created a 2016 return using TurboTax Online, then you will need to create a new login for a second return. Otherwise, you will overwrite the return you have already created.
You can only import a previous year's return into TurboTax Online if it was also created using TurboTax Online. You would have to create the return using the same login that you used for the 2015 return. If this is not possible, you will have to check the various worksheets from last year's return to see if there were any carryovers (Net Operating Loss (NOL), passive activity loss, capital loss carryover, AMT from previous years).
TurboTax Desktop is much more flexible. It is capable of importing .pdf files, as well as files from other software. You can also e-file up to 5 tax returns using the desktop edition. For more information, see the FAQ below.
https://ttlc.intuit.com/replies/3302290
The following FAQ explains more about importing into the online edition.
https://ttlc.intuit.com/replies/3301662
