In finder when you right click on a file the popup menu has an option called “Open With”. This lists all of the applicable applications that can process this file.
If this list becomes too large or contains duplicates you can remove the applications and then rebuild the list using the following command line.
To rebuild the list open a terminal and enter this command:
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user