I'm using Acrobat Standard DC 2015. I was using Acrobat 9 Standard. I work with several PDF files that are protected by "protectedpdf" (Vitrium Systems). These files use an online unlock with a password. With acrobat 9, I entered the password for each file, unlocked it and checked "stay logged in". With Acrobat DC 2015, each time I enter a password for one of the files, it tries to use it for all the files and when I open a second file, I get an error.
These files are ICC building code books. Each code has a different password. I usually have several codes open at the same time. I've used them for years without problems. This problem started when I changed to Acrobat Standard DC.
Another problem came up today; even if I re-enter a serial number, I'm locked out of the file ("installed on too many computers"). I am sure I can work this out by contacting the code vendor or uninstalling and reinstalling the code books, but that's not really functional. Any ideas? Thanks.
Acrobat 9 had several security holes which were fixed over time in subsequent versions. It is quite possible that the additional software (Vitrium Systems, and I do not know what that is) relied on some Acrobat 9 behavior which is not supported anymore. I suggest that you contact Vitrium Systems.and ask them what's going on.