It would also be advisable to use a PDF viewing program other than Acrobat Reader. It was never the most secure program to begin with and now that XP has reached EOL Adobe is probably glad to have an excuse not to continue making sure Acrobat Reader works with XP. Just say it's no longer supported, upgrade to a newer version.
Even though I think it kind of jumped the shark with version 5, Foxit Reader is still probably one of the best alternative PDF viewers out there. Haven't come across a PDF file yet it can't read, it has a fairly extensive set of annotation tools and even if it has bloated rather significantly in it's later years, it still weighs in at probably under half of Acrobat Reader in every important metric.
Of course there's also Firefox, which now has its own integrated PDF viewer. It's fairly bare bones, but if all you need is the ability to view and print, it works a treat. I kind of like that it doesn't respect restrictions on copying and pasting text from the PDF. I have copies of some public records obtained via a FOIA request and they have that property set -- despite them being a matter of public record, meaning I should be free to do use extracts as I see fit -- but viewing them in Firefox allows me to copy and paste all I like, even if the text selection code is one of the rough edges on the PDF viewer still. I think Google Chrome has something similar.
How long either will be supported on XP is a bit of an open question, so migrating to Linux or any newer version of Windows would be very strongly advised.