If you used one of the TurboTax desktop CD/Download editions for tax year 2020 then you need to transfer the tax data file to the 2021 online edition. The tax data file has a file extension of .tax2020 and is stored by default in the Documents directory and in the TurboTax folder.
You cannot transfer a PDF of the 2020 return to the 2021 online editions if you used the TurboTax desktop editions for tax year 2020.
See this TurboTax support FAQ for transferring a 2020 tax return to a 2021 tax return using the online editions - https://ttlc.intuit.com/community/entering-importing/help/how-do-i-transfer-last-year-s-return-into-...
