There is not a way to attach a PDF document to an electronically filed return using TurboTax.
If your VIN number is not found in the database, then first double-check your entry against a photo of your actual VIN number. It is possible that maybe a zero was entered as the letter O or vice versa. If that doesn't work, then the dealer may have made an error when entering the information into the system used by the IRS.
Your only course of action if you entered everything accurately is to file the return by mail to include a copy of the Bill of Sale showing the correct VIN.
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