It might also depend on the program that made the PDF. I got a new patient form in PDF but when I tried to edit it in Acrobat Reader it shoved the words about which was no good.

Then I downloaded a trial copy of the latest version of Acrobat Reader and it still did not work. So I cancelled the subscription because $20 a month is a bit pricey for something I use once or twice a year.

And it deleted my previous pre-subscription version of Acrobat. But to Adobe's great credit one of their chat support persons pointed me to my product and I was able to download and register my paid for version.