Hi it's me again, so glad to have this site to come to with my little 'pea' brain ?'s!!!!

I have an email with a PDF attachment that IE can't or won't open. It says that my security settings doesn't allow this program to be opened. I checked the security settings and I have no idea how or what to change. It's says "trusted sites" but this is not a site, it's a document from a email address that I have received attachments before. About a month ago, my computer was upgraded and ever since then I have had some problems I never had before what gives?!!! Why do I have computer when I don't know how it works, you might ask, but I drive a car and I don't know how it works, when there is a problem, I take it to the experts, same as here!! Thanks in advance!!!