Does anyone know if I can still get old versions of Acrobat to work and register?

No idea if the old versions of Reader work in Windows.....but the very last, final Linux version (Reader9) works great for me in 'Puppy' Linux!

It's a big program by Puppy standards (which tries to keep applications as small as possible), but it just does everything I want it to.....including annotation, which many Linux PDF apps won't handle very well, for some reason.

Mike. ;)
On an unrelated note (somewhat), Acrobat 5.x was far and away the best version of this venerated program (in my opinion, for what little it's worth). The bloat started creeping in with 6.x, and it seemed to get worse with every subsequent version. I would still be using Acrobat 5.x if it wasn't for modern .pdf files rapidly losing compatibility (though it should be possible to restore the incompatible files with a converter whereby 5.x can read them properly). Even Foxit Reader, which became my favorite program for reading .pdf files after Adobe started filling theirs with bloatware, is now significantly bloated itself. I never understood that!
If you are talking about Acrobat Pro, Adobe turned off the activation servers around 2016. If you had before then registered your licensed activate copy on Adobe's website, it's possible to download a no-activation required installer plus working serial. Keep in mind it's probably phoning home everytime you use it, so if you want to use that installer and key on 2 computers, Adobe may decide to deactivate all installs with that serial and invalidate the serial (why I haven't tried that).

I found out about this at work while moving my copy of Acrobat Pro v8 to my new PC (Win7). V8 was the last one before the MDI was removed. Without MDI, Acrobat Pro is useless (for me). Fortunately I had registered the program around 2010 and was able to get the no-activation installer and serial. It works fine on the new machine.

At home, I suffer with the feature lacking free Acrobat 7 Pro. I would love to have v8 installed. I have a legal purchased retail copy and license of v8, but I never registered it on Adobe's site, which means I can't get a serial for the no-activate installer.... I spoke with their tech support and the basically said in many words "tough". There are no cracked copies of v8 that don't have a virus, so I'm out of luck.