How do I attach additional documents to an e-file return?

What documents are you trying to attach?  You cannot attach documents to an e-file.   If the IRS wants additional information from you after you file they will ask for it.

I am a trader in securities. Each year I file a paper tax return so I can add supplemental documentation of the qualifications for this status and also send all trades to document. This avoids any doubt as to qualification.

My 2019 refund has still not been paid because the IRS is so far behind on paper returns. Mine is 10 months old now. Thus I wanted to avoid paper with a 2020 e-file. Thanks.

Ok yes, as xmasbaby0 stated above, there is no way to send additional documentation when you e-file, unless the IRS requests it from you. Unfortunately, the only way would be to mail your tax return in if you need to attach additional documentation.