Adobe Reader not functioning on new computer for pdf documents

I don't use Adobe Reader currently but I have needed it in the past. At one time Preview was abysmally slow in handling very large PDF's. I no longer have to deal with those so don't know if that is still the case.

So, what do you mean by “Adobe Reader not functioning”? As has been pointed out the current version of Reader works with Big Sur. Have you updated both Big Sur and Adobe Reader to the latest versions?

And when I tried to convert a PDF to Word using Adobe Reader I was forwarded to Adobe’s website and told I had to upgrade to Acrobat Pro to convert. Is that what you are experiencing. If so then it would appear Adobe is now charging for the conversion.

There is an online PDF converter that I have used with success. https://online2pdf.com but I don’t know about security or privacy.

Finally, Word can directly open PDF files which you can then save as a Word document. Have you tried that?

Adobe Acrobat Pro DC will convert PDF to Word, and so will MS Word 16.31 or later. Adobe's Acrobat Reader DC has no inherent capability to convert PDF to Word documents itself, but if you have a paid subscription with Adobe, then Acrobat Reader DC will allow you to upload that PDF to Adobe, where the actual PDF to Word conversion takes place.

I am using the current Adobe Acrobat Reader DC on macOS 11.6 and it works fine. I do not feed PDF to Adobe for conversion to Word though.

Adobe Reader works with the current version of macOS Big Sur 11.6.

Are you running the latest version of Adobe Reader downloaded from https://get.adobe.com/reader/ ?

Why are you even trying to use Adobe Reader when Preview is pre-installed on your computer? I've never had a need to use AR when Preview is there in over 20 years of Mac usage.