Unfortunately the PDF upload for 1099-B is only available in TurboTax Online. However, check your transaction types; you may not need to mail anything.
Here's more info on How to Enter a Summary in Lieu of Individual Transactions. The IRS has copies of your 1099-B's anyway.
Some users have reported using TurboTax Online to attach their PDF's and then transferred their return into TurboTax Desktop, but we haven't documented their results. If you try this, be sure to save a copy of your original return.
Here's some info on How to Transfer from TurboTax Online to TurboTax Desktop.
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