@Alfred O Johnson Any pdf reader should open a pdf file. Which program didn't open them? Are you talking about the Turbo Tax program? You need the tax file to open in the program. The tax files end in .tax2018, .tax2019, .tax2020 etc. Do you have any of those? The tax files should be in your Documents in a Turbo Tax folder. You should also have the pdf files of each year. Or search your computer for all files ending in .tax.
If you can find your tax data file ending in .tax2020. Did you have to reinstall Turbo Tax program? After you get the program reinstalled the first thing to do before you open your tax return is to update the program and install any state programs you had. Then open your .tax2020 file. So you first might need to start a fake return to be able to download the state program (go to FILE - NEW). Enter some basic information, then go to the state tab and download the state program. Then try to open your existing return, go to FILE - OPEN
Who do you need a 2020 copy for? The IRS or someone else? Did you file 2020? Can you get a copy from the IRS?
Request a transcript from the IRS
https://www.irs.gov/individuals/get-transcript
For $43 you can get a copy of your tax return
https://www.irs.gov/pub/irs-pdf/f4506.pdf
