How to fix Internet Explorer that Opens Automatically?

I have never experienced this type of problem before. My internet explorer is opening automatically time and time again. Basically I am using Firefox 3.6.17 and use Internet Explorer occasionally. I guess this is happening for virus attack and checked every drive by kaspersky antivirus and it is a licensed version.
But not getting any virus and nothing has changed. I can’t uninstall internet explorer because I need to use it to open and print some special PDF format documents which is not compatible to any other web browser. I have also searched on the internet for the solution but unable to find it.
I found this site very helpful and hope there will be a solution.
