How do I sign the downloaded PDF file
And where will I send it to
Accepted? Did you e-file the 2020 tax return? If so, there is nothing further that you need to mail to the IRS.
What was Accepted? Did you efile? If you efiled you do not mail in the pdf. That is the great thing about Efiling. Nothing to mail in. Or explain more why you need to mail your return.