As far as I know, there is no provision for attaching a PDF.
I'm sure you meant Form 8453. There is no Form 8953. Form 8453 is used for paper attachments that you have to mail to the IRS after you e-file your tax return. If a PDF attachment is included in the e-filed return you don't need Form 8453. TurboTax will produce the Form 8453 for you if it is needed.
