When e-filing a tax return you cannot attach any type of document.
If you need to include a document that is not included in the TurboTax program then you will have to print and mail the tax return.
See this TurboTax support FAQ for how to print and mail a tax return when using the online editions - https://ttlc.intuit.com/turbotax-support/en-us/help-article/printers-printing/print-mail-return-turb...
